
Class XHiM 
Book . fl5 2._ 



ghtF I'BIS 



COPYRIGHT DEPOSrr 




THOMAS A. EDISON 

Copyright by W. K. L. Dickson 



THE 



STANDARD MANUAL 



OF 



DYNAMOS 



AND 

PRACTICAL APPLICATION OF 
DYNAMO-ELECTRIC MACHINERY 

By Carl K. MacFadden 

Associate Member American Imtitute Electrical Engineers 



AND 



Wm. D. Ray 

Associate Member American Institute Electrical Engineers 
Vice-President Chicago Electrical Association 

19 15 



REVISED Yimmm EDITION 




Laird & Lek, Inc., Publishers 

CHICAGO 






Copyright 1915, by Laird & Lee, Inc. 



Copyright 1906, by William H. Lee. 



Copyright 1S95, by Laird & Lee. 



Copyright 1894, by Date & Ruggles. 



m -8 !9I5 
CIA393896 






Index. 

CHAPTER I. — ei.e;me;ntary data . - 7 

Units of Electrical Measurement. 
Ohms Law. 

CHAPTER II.— MAGNKTISM AND INDUCTION - I5 

Methods of Current Generation. 

CHAPTER III.— THEORY OF DYNAMOS - - 20 

Action of Commutators. 
Methods of Dynamo Control. 

CHAPTER IV.— CURRENT DISTRIBUTION - - 4I 

Losses in Copper Conductors. 
Fuses and Safety Cutouts. 

CHAPTER V. — TRANSFORMERS - - - - 62 

Construction and use. 
Alternating Current Distribution. 

CHAPTER VI.— TYPES OF DYNAMOS - - - 76 

Direct and Alternating Current. 
Their Application in Practice. 

CHAPTER VII,— CAUSES of troubi^e in dynamos 88 
Their Remedy and Prevention. 

Methods of Testing for Faults, etc 



INDBX 

CHAPTER VIII.— ARC I.AMPS - - . - loj 
Direct and Alternating Current. 
Various Types and Makes. 
Incandescent Lamps of Various Types, 

CHAPTER IX. — EI.KCTRIC MOTORS - - - 121 

Transmission of Power Dynamos. 
Direct and Alternating Current. 
Various Types of Motors. 
Street Car Systems. 
Methods of Motor Control. 

CHAPTER X.— STORAGE BATTERIES - - - 139 

Various Types. 

Their Care. 

Directions for Charging. 

CHAPTER XI.— EI.ECTRIC HEATING - - - 154 

Electric Cooking. 
Electric Welding. 
Electric Metal Working. 
Station Instruments. 
Switchboards. 

HORSE POWER EQUIVALENTS - - - 165 

COPPER WIRE DATA 166 

Copper Wire Table. 
Safe Carrying Capacity. 



Preface. 

Our aim in bringing out this little book has been to 
reach a class of readers who, realizing the need of a gen- 
eral fundamental understanding of the application of 
Electricity, will read with some benefit, we trust, a few 
descriptions of the modus operandi of the most generally- 
used class of Electrical Machinery. 

It has not been our intention to take up the subjects 
treated on, in any but the most simple and as we believe, 
the most easily understood way. 

It is becoming more necessary each year for the well 
qualified steam engineer to be somewhat familiar with 
Dynamo Electric Machinery in order to advance in his 
calling. A partial understanding at least is now or soon 
will be almost a necessity for those engaged in nearly all 
branches of engineering work. There is hardly a pro- 
fession which electricity in some way has not entered. 
The vast majority of the men in charge of our practical 
work have never had the advantage of a technical educa- 
tion and are therefore unable to follow the advances that 
are so rapidly being made. 

The volt, ampere, and ohm and their relations to each 
other are the first stumbling blocks and the cause is easily 
seen by inspecting a few books for definitions of these 
words. 

We have endeavored to impress as much as possible, 
the formula expressing Ohms Law, 

E 

R 

on which all calculations necessarily take their start. A 



6 PREFACE. 

thorough understanding of the relations of the volt, 
ampere and ohm to each other, is without doubt the 
foundation of all electrical knowledge. 

We have also endeavored to keep up to the times and 
believe we give some interesting descriptions of modem 
electrical apparatus, which will be of value to those whose 
main source of light on electrical matters come from cat- 
alogues and newspapers. 

The dynamo tender, unless partially conversant with 
the principles on which his machinery operates, will often 
be perplexed at even the most trivial troubles to which a 
dynamo is subject. A motorman on our usual electric 
street cars, could often lessen motor repairs to a great 
extent by obtaining even an elementary understanding of 
the motors' action. An understanding of the proper dis- 
tribution and installation of electric wires would be the 
means of averting many thousands of dollars loss each 
year by fire from electrical causes. 

There are many good books on the various branches of 
electrical work but they are too often of such a technical 
nature as to bar the uneducated reader from obtaining 
much benefit from them. We hope that a close study of 
the following pages will place the average beginner on 
such a foundation as to make the other more complete 
electrical books more easily understood. 

CarIv K. MacFadden. 
June I, 1894. Wm. D. Ray. 



ElyKMENTARY DATA. 



CHAPTER I. 



ei.kme:ntary data. 



What is electricity? A question often asked and prob- 
ably never as yet clearly answered. 

Those interested in the practical field, find it almost 
impossible to keep up to the times, in regard to the laws 
that govern its generation and control. We know that 
by means of certain combinations of coils of wire and 
magnets or by means of chemical action, we can produce, 
we may say, electricity. 

We must be content if we master a few leading laws 
governing the generation and application of the Electric 
current. Let the Scientists and Philosophers discuss the 
question as to what electricity is. In dealing with the 
simple electric current that is generated by dynamos, 
batteries, etc. , we will find that there are several broad 
and easily understood laws that govern its practical 
applications. These laws hold good in all cases and un- 
der all conditions, and should be thoroughly understood 
by anyone desiring to learn even the first and most sim- 
ple effects of a flow of electric current. 

Probably the easiest way to understand this law will be 
to take a simple case of a pump connected to a loop of 
water pipe. The pipe is filled with water and it is evi- 
dent that if the pump is started there will be a circulation 
of water from the pump through the pipe and back into 



8 



KI^KMENTARY DATA. 



the pump again. The pump furnishes the power to move 
the water in the pipe — and it is evident that the water 
moves through the pipe owing to the pressure exerted by 
the pump on the water. In (figure i) an open tank, 
(d) is shown into which the water flows from the pipe. 
The pump takes the water from the tank to keep the 
pipe filled, and the speed of the water through the 




FIGURE I. — PUMP FORCING V7ATER THROUGH PIPES. 

pipe and therefore the quantity of water passing through 
the pump and pipe in a minute of time, will depend on 
the pressure given the water by the pump. 

If we double the pressure of the water and the friction 
or resistance to the flow of water in the pipe remains 
constant, the quantity of water handled by the pump 
will be doubled. In other words by increasing the pres- 
sure, w^e increase the quantity of water passing through 
the pipe at exactly the same ratio. Now if we found 
that a guage placed at (a) would have to register 50 lbs. 
pressure to make 100 gallons of water pass through the 
pipe in a minute, it is evident that if the friction in the 
pipe remained the same, that 100 lbs. pressure ought to 
put 200 gallons through the pipe. It is also evident that 



EI/EMKNl'ARY DATA. 9 

if icx) feet of pipe a certain size oflFers a definite amount of 
friction, that twice the length of pipe would have two 
times the friction or resistance to the flow of water that 
the loo feet has. Thus to put loo gallons of water a min- 
ute through a pipe will take yi the pressure required to 
force 200 gallons through the pipe. This example may 
serve the purpose of illustrating the principle of the flow 
of current from a source of electricity. We will let the 
dynamo take the place of the pump, which will generate 
the pressure to send the electricity through the circuit 
which may consist of lamps, etc., connected by means of 
conducting wires. The friction in the pipe is represen- 
ted by the ''resistance" of the wire and circuit, and the 
amount of water used, represent the quantity of the cur- 
rent of electricity. 

Instead of using the pound as the unit of water pres- 
sure we will use the term ' 'volt' ' which is the unit of 
electrical pressure. We also have a term which denotes 
the unit of ' 'resistance, which is the equivalent of ' 'fric- 
tion" used in the illustration ot the pump and pipe. The 
unit of resistance is called the "ohm." 

Then lastly the quantity of current in electricity is 
measured by the unit of current quantity, the "am- 
pere. ' ' This is the quantity of current that a pressure of 
one volt will force through a resistance of i ohm. 

The resistance of a conductor of electricity varies not 
only with its size or cross section but also with the ma- 
terial of which it is made. Silver, when pure, is the best 
conductor of electricity known, but copper, when pure, 
nearly approaches silver and is so much cheaper that it is 
used in nearly all cases to distribute current for practical 
purposes. 



ro EI^HMKNTARY DATA. 

The metals in their order for conductivity are as follows: 
Silver, Copper, Gold, Aluminum, Zinc, Platinum, Iron, 
Lead, German Silver, Platinum Silver alloy and Mercury. 

In practice the wires or conductors to carry current are 
either designated in size by their diameter in thousandths 
of an inch (or mils) or by the sectional area or cross sec- 
tion of the wire expressed in circular mils or by the size 
in number, as measured by the Standard American or 
Brown & Sharp Wire Guage. 

A circular mil is a circle ^q^qq inch in diameter. 

As in the case of pump, the higher the pressure in 
volts at the dynamo, the larger quantity of electricity 
(expressed in amperes) will be put through a circuit 
which has a resistance (expressed in ohms) to the flow of 
current. 

Thus if I volt pressure will force i ampere of current 
through a circuit having i ohm of resistance, it will take 
5 volts to force 5 amperes thiough this same i ohm of re- 
sistance and if this resistance is increased to 2 ohms, the 
pressure would have to be 10 volts to force 5 amperes of 
current through it. 

It will be seen that these terms are dependent on each 
other and their relation to each other is expressed by 
what is known as Ohms Law which is expressed: 

Current Pressure in Volts E 

in = ^ or C = — 

Amperes Resistance in Ohms R 

**C" standing for current, "K" for electro-motive force 
or volts, and ''R" for resistance expressed in *'Ohms.'* 
This relation C=B/R must be remembered for it is the 
fundamental law of the governing of electric currents, 
and is used as a foundation to obtain all of the more com- 



EI.KMENTARY DATA. II 

plex formulas known to the Electrical Engineers. 

Take the simple case of a certain make of incandescent 
lamp, the resistance of the lamp in question is found to 
be 200 ohms The pressure of the circuit on which this 
lamp is designed to run is 100 volts, and according to 
Ohms law the current in amperes which 100 volts pres- 
sure will force through 200 ohms of resistance is ^gg or 
yi which is the number of amperes such a lamp would 
allow to pass through it if current at 100 volts pressure 
was applied. 

It will thus be seen that it is a very easy matter to ob- 
tain any one of these quantities, provided we have the 
other two given, by a simple multiplying or dividing of 
the two known quantities. The relations to each other 
are expressed 

E E 

C= — , E=R X C, and R= — . 

R C 

There is still another term with which the practical 
man is brought in contact and that is the unit of power, 
the *'watt." This watt is the /(^ze'^r represented by the 
passing of i ampere of current through i ohm of resis- 
tance and can always be obtained of any current by mul- 
tiplying the number of volts by the number of amperes. 

Thus in the incandescent lamp before spoken of, the 
watts used by the lamp would be 100 (volts) x^ (^inp) = 
50 (the number of watts), this being the amount of elec- 
trical energy necessary to be applied continually to keep 
the lamp burning. Such an incandescent lamp would be 
termed "a 50 watt incandescent lamp." An arc lamp 
which needed a current of 10 amperes at a pressure of 
50 volts to keep it in operation would be termed a * '500 
watt arc lamp". 



12 



ELEMENTARY DATA. 



There are two entirely diflferent methods of distribu- 
ting current to lamps etc., connected to dynamos. 

The plan illustrated by means of the pump in (figure i) 
may be seen as applied to a dynamo and lamps in (figure 
2) (a), in which the dynamo D supplies current for lamps 
L, and is known as the Series System. It will be seen in 
plan (a) that the lamps are connected in "series" that 
is, the current which passes out from the positive (-|-) 
D D D 




d) 
d) 
(J) 
O) 
0) 



(!) Q 
(!) a) 
(!) Q 




^ 
^ 



^ 



^ 



^ 
^ 



■^ 




Series (a) Multiple or Parallel (b) Mulliple Series {c) 
FIGURE 2. — SYSTEMS OF CURRENT DISTRIBUTIOIT. 

brush of the dynamo must go through the whole series 
of lamps before the negative ( — ) brush is reached, the 
number of amperes flowing through the v/ire will be found 
to be the same at whatever point it is measured, but the 
pressure in volts will vary with the number of lamps 
through which current is forced. If each of the lamps 
required lo amperes of current to bring it up to candle 
power, and it took 50 volts pressure to put 10 amperes of 
currei • ^Wough it, or in other words, if the lamp had 5 



ELEMENTARY DATA. I3 

ohms resistance, then the dynamo would have to generate 
50 volts for every lamp in the series of lamps or on a 10 
lamp circuit the voltage would be 500, 20 lamps 1000 
volts and so on. Such a system of lighting is used in 
operating the usual type of * 'Series arc lamps." The 
current in amperes remains nearly constant, but the 
voltage at the dynamo varies with the number of lamps 
through which it has to force current. 

Plan (b), figure 2 shows the Multiple System or the 
system of placing lamps in parallel or multiple arc. The 
dynamo (D) furnishes current of a uniform pressure to 
lamps (L) connected to the mains marked (-[-) and ( — )the 
current from the dynamo however varies as to its quan- 
tity in amperes, on the number of paths through the 
lamps from the positive to the negative mains. This 
plan of current distribution is used in furnishing current 
to the usual incandescent lamps, or in any other work 
requiring a uniform pressure or voltage. It will thus be 
seen that the multiple system is the opposite from the 
series system in several ways. In the series system the 
larger the number of lamps the higher the pressure in 
volts, although the current in amperes remains constant, 
while in the multiple system the voltage remains prac- 
tically uniform and the amperes given out by the dyna- 
mo varies with the number of lamps connected between 
the mains. 

The Multiple-Series plan of distribution is a combina- 
tion of both the previous methods and is shown in plan 
(c) figure 2. This system of wiring is used to operate arc 
lamps on incandescent or constant potential circuits and 
in the other special places which will be spoken of later 
on in Chapter IV. 



14 KI.EMKNTARY DATA. 

746 watts are equal to i electrical horse power and by 
dividing the output of a dynamo in watts by 746 we can 
obtain the output of the dynamo in electrical horse- 
power or E. H. P. 

1000 watts = I kilo watt and is a term generally used 
to give the rating of generators or dynamos. The abbre- 
viation K. W., is used to express kilo-watt. It is evi- 
dent that the term kilo- watt as used to describe a dynamo 
does not denote the voltage, or the current in amperes, 
which the dynamo may be designed to generate. It sim- 
ply means, for example, in a i kilo watt generator, that 
the generator has a capacity of supplying 1000 watts of 
electricity, which may be represented by i ampere at 
1000 volts pressure, 1000 amperes at i volt, 10 amperes at 
100 volts, 100 amperes at 10 volts or any other combina- 
tion of current that equals 1000 watts, as the case may be. 

A proper description of such a generator would be, for 
instance, a i kilo watt, 100 volt generator, which of 
course lets us know that such a dynamo will generate 10 
amperes at the 100 volt pressure, thus making one thous- 
and watts or one kilo-watt. Hence Watts or W. =C x E 
the product of amperes and volts. 

The instruments used for measuring electrical pressure 
in volts are generally called voltmeters, or pressure indi- 
cators. Those for measuring amperes or quantity are 
called ammeters. 

The resistance in ohms is measured usually by means 
of an instrument called the Wheatstone bridge, or rarely 
an ohmmeter. 

Wattmeters are used for measuring watts, or the pro- 
duct of volts and amperes. 



MAGNETISM AND INDUCTION. I5 



CHAPTER II. 



MAGNETISM AND INDUCTION. 



Inasmuch as the generation of dynamo electricity is 
effected by means of the action of magnetism, it is well 
to take up the subject of magnets first. 

A magnet, as known to practice, is a piece of iron or 
steel, which has the power of attracting other pieces of 
iron to it. There are two types of magnets, permanent 
magnets, and electro-magnets. A permanent magnet is 
usually made of hard tempered steel, which after having 
been brought under the influence of some magnetizing 
apparatus, retains a more or less amount of magnetism. 
We often see them in horse-shoe form, known as horse- 
shoe magnets. Large permanent magnets, however, are 
expensive to make, and are extremely weak in compari- 
son to their weight, and in addition they seldom hold 
their magnetism for any length of time. 

The other type, known as the electro-magnet, is 
quite a diflferent thing. If a piece of iron has wound 
around it, a few turns of insulated wire, and a 
current of electricity be passed through the wire, the 
iron immediately will be magnetized, and will remaij. 
magnetized as long as the current passes through tW 
wire. The moment, however, the current through 1 le 
wire is stopped the iron is no longer magnetized. Tl as 



l6 MAGNETISM AND INDUCTION. 

it is seen that the current in passing around the iron has 
an efifect on it, and magnetizes it. 

The amount of magnetism shown by the iron centre of 
the coil will depend on two factors, the number of 
turns of wire around the core of iron, and the number of 
amperes of current passing around through the turns. 
Thus with lo amperes passing around the core, 20 turns 
of wire will have twice the magnetizing power that 10 
turns will have. . The effect will depend on what is 
known as the number of ' 'ampere turns' ' in the coil of 
wire, the ampere turns being the product of the number 
amperes and turns, thus, if we have 10 turns and 10 am- 
peres passing through them, we have a coil of 100 
ampere turns, which will have J4 the effect that 200 am- 
pere turns will have. It is evident, that 100 turns with 
one ampere passing through them, will have the same 
effect as 50 amperes and 2 turns, or 100 amperes and one 
turn, each of the above quantities being equal to . "X) am- 
pere turns. 

We have practically no limit as to the strength of the 
magnet we may construct. The very powerful magnets 
used in dynamos lately constructed, are made by winding 
an immense number of turns on large iron cores, and 
then sending currents of electricity through them, thus 
making a large number of ampere turns, and producing 
an immense magnetic effect. 

Iron has been spoken of as the cores for the magnets 
because it is the metal found to be capable of carrying 
more magnetism than any other. In any coil of wire 
carrying an electric current we may imagine a large 
number ''lines of magnetism" being generated by the 
current, each line starting from the end of the magnet 



MAGN^ISM AND INDUMION. 



17 



called the positive end and taking a path through the air 
or some magnetic material back to the other end of the 
coil called the negative end. These little loops are 
thrown out from the end of the coil and will follow the 
easiest path back to the other end, thus completing a 
magnetic circuit. A permanent magnet made of hard- 
ened steel throws out these same little loops from its 
poles without being excited by means of the passage of a 
current of electricity arou-nd it. 







FIGURE 3. — KlvKCTRO-MAGNET AND ARMATURE SHOW- 
ING WNES OF MAGNETISM. 

If a piece of iron or steel is placed in such a position 
with relation to the coil as to be in the magnetic influ- 
ence or * Afield," a large number of these lines of magnet- 
ism will take the path through the iron in preference to 
that through the air owing to the fact that iron will 



l8 MAGNETISM AND INDUCTION. 

carry lines of magnetism better than air or any other 
material. The iron under these conditions will tend 
to assume the position in which the largest number of 
the lines of force or magnetism will pass through it, and 
for this reason iron is * 'attracted" to the coil or mag- 
net. Some iron carries these lines thousands of times 
better than air. Figure (3) shows the action on a horse- 
shoe magnet made of soft iron, having a coil of wire on 
each limb. 

The nearer the armature or * 'keeper" of the horse-shoe 
magnet approaches the ends of the magnet, the stronger 
will be the pull, owing to the increased number of lines of 
magnetism it carries. A compass needle points north and 
south because in that position the metal of the compass is 
parallel to and is carrying more of the lines of the Earth's 
magnetism through it, than at any other position. 

If a coil of wire is wound on a hollow spool of wood or 
other non-magnetic material, and- a current of electricity 
be passed through the coil, it will be found that a piece 
of iron will be drawn up into the coil of wire and tend to 
assume a central position in the coil. On stopping the 
flow of current through the coil, the iron core will no 
longer be attracted. When the core of the coil or *'sel- 
onoid" as it is called, is in its centre, it is carrying the 
maximum number of lines of magnetism. 

The selonoid is a form of magnet often used in the 
manufacture of arc lamps, etc. , and is adapted for this 
purpose on account of the large movement of the core 
compared to that of the armature, or keeper of the usual 
type of electro-magnet with an iron centre. 

There is still another wonderful effect of magnetism, 
that of induction. If a magnet be moved about in the 



MAGNETISM AND INDUCTION. I^ 

vicinity of a coil of wire whose ends are connected to a 
means for measuring the passage of an electric current, it 
will be found that a current of electricity will be gener- 
ated in the wire of the coil, and that it flows only when 
the magnet is being moved near the coil. Also, that as 
the magnet moves toward the coil» that the current flows 
in one direction through the coil, and as it is being pulled 
away, the current flows in an opposite direction. 

By arranging a suitable set of coils and magnets, in 
such manner that the coils pass in front of the magnets, 
we may be able to generate strong currents of electricity, 
and in fact, all dynamos and generators are operated on 
this plan. The usual method employed ib to so mount 
an electro magnet, called the field magnet, that there is 
a break in the iron magnetic circuit, across which the 
lines of magnetism will pass in completing their circuit. 
In this gap in the magnetic circuit, an armature con- 
sisting of a number of coils of insulated wire mounted on 
a shaft, is revolved by means of power applied to it. As 
these coils of insulated wire move through the lines of 
magnetism, currents of electricity are generated in them 
which are carried away from the armature, to the lamp, 
etc., to which the dynamo is connected. 



30 THEORY OF DYNAMOS. 



CHAPTER III. 



THEORY OF^ DYNAMOS. 



An electric generator or dynamo is a combination of 
coils of wire and magnets, which have a movement with 
relation to each other and which, when supplied with 
suitable mechanical power will generate currents of 
electricity. 

In practice, they consist without exception of an ar- 
mature in which the currents of electricity are generated, 
and a field magnet or magnets which furnish the lines of 
magnetism, through which the coils of wire on the arma- 
ture pass, and thus generate current. 

The armature may be, and usually is, the moving part; 
but this is not by any means a necessary thing, for the 
field magnets may be made the moving part with the 
armature stationary and accomplish the same result. 
At present the stationary armature is found only on a 
few types of dynamos which are usually used for gener- 
ating alternating currents. It has been shown that the 
movement of a coil of wire with its ends connected, in 
the vicinity or magnetic field of a stationary magnet, 
will generate currents of electricity in the coil. If the 
coil of wire approaches the magnet, the flow of current 
will be in one direction, and if it is drawn away, the 
current will flow in an opposite direction through 
the coil. If the coil is held stationary near the mag- 



THEORY OE DYNAMOS. 



21 



net, no current will be generated in it. This is all 
caused by the coil of wire passing through, or * 'cutting'*, 
the lines of magnetism. The current generated, depends 
however, on several factors. In the first place let us 
construct, for illustration, the simplest possible form of 
a dynamo. To furnish the lines of magnetism, we will 
use a simple steel horse-shoe shaped permanent magnet, 
M, see figure 4. 




I«'IGUR:e 4.— SINGI.K I^OOP ARMATURK WITH COLLECTOR 

RINGS, REVOLVING BETWEEN POLES OF 

PERMANENT MAGNET. 

On a shaft we mount a coil of wire consisting of one 
convolution, the ends of which are connected to insu- 



22 THEORY OF DYNAMOS. 

lated rings mounted at one end of the shaft and on which 
two brushes bear, and thus connect the coil of wire to a 
suitable measuring instrument (a) . In the diagram we will 
assume that the lines of magnetism are being concentra- 
ted between the ])oles N end S; N being the north and 
S the south. Thus if the coil of wire on the armature 
is revolved on its shaft, it is evident that with the coil in 
the position shown, will have Its right hand half moving 
down before the pole S, and the left hand half moving 
upward before the pole N, and since we assume that 
there are an immense number of lines of magnetism 
flowing through the space from N to S, it is evident 
that the moving coil must *'cuf these lines, and 
it is this action that generates current, or to be more 
correct, generates electrical pressure which expends 
itself in creating a flow of current, the amount depend- 
ing on the resistance of the circuit. Assuming that the 
lines of magnetism from the permanent field magnets, 
remains constant, we will find that the electrical pressure 
generated, and thus the current will depend on simply 
the rate at which these lines of magnetism are cut, if at 
looo revolutions per minute the coil of a single turn 
will generate 5 volt pressure, 2000 revolutions per min- 
ute will generate 10 volts pressure. The direction in 
which the current will flow, will depend on the direction 
of movement of the conductor through the lines of mag- 
netism. 

In a simple loop, whose ends are connected to rings, 
mounted on shaft as shown in figure 4, the current 
through half a revolution will flow through the coil in 
one direction, and in the remaining half revolution the 
current will flow in an opposite direction. Thus in a 



THEORY O^ DYNAMOS. 



23 



complete revolution, the current will flow first in one 
direction, and then reverse and flow in an opposite direc- 
tion, and in this way produces what is known as an alter- 
nating current. This alternating type of current can only 
be used for certain kinds of work, and to so arrange ths 
connections that all the impulses or waves of current 
generated in the armature will be given out in one direc- 
tion, a commutator is necessary. The action of the com- 



C- 




FIGURE 5. — SINGlvE lyOOP ARMATURE ON IRON CORE 
WITH COMMUTATOR AND BRUSHES. 

mutator may be understood from study of figure 5, 
which shows the same loop x>f wire between the poles of 
a magnet, as v/as shown in figure 4, with the exception 
that instead of rings mounted in the shaft, with brushes 



24 



THEORY 01^ DYNAMOS. 



bearing on them a split ring is shown, each half of whicV 
is connected to a terminal of the single armature coil of 
one turn (c). The two half rings are insulated from each 
other and from the armature shaft, and the action may 
be described as follows: — From the point (A) figure 5 
to the point (B) which is yi revolution, the current 
flows in such a direction as to make the brush (-]-) a 
positive brush, that is, the current flows from -|- to — , 




FIGURE 6. — ALTERNATING CURRENT WAVE. 

the current generated depending on the rate at which 
lines of magnetism are being cut by the loop of wire. 
The current with the loop at the line ( A-B ) will be 
zero, for this is the point at which the current is revers- 
ing its direction in the loop, owing to the fact that 



THEORY Olf DYNAMOS. 25 

the direction in which the loop cuts the lines of mag- 
netism is being changed. From this position on dotted 
line A — B, the current will gradually rise to a tnaximum 
when the loop is on the line C — D, which is the point at 
which a certain given movement of the loop will cut the 
greatest number of lines of force. The rise and fall oi 
current in an alternating current circuit may be shown 
readily by the cut in figure 6. The line A — B repre- 
senting the zero line or line of no flow of current in the 
coil. The distance from i to 2 represents one complete 
revolution and the curved line C represents the current 
produced by the revolving loop. The portion of the 
curved line above the zero line represents current flow- 
ing in a positive direction and the portion below the line 
will represent the negative flow of current. The total 
curve from i to 2, represents one complete alternation, 
which in the combination shown in figure 4, means 
one revolution. If we had the coil making 2000 revolu- 
tions per minute, there would be 2000 of such waves as 
shown in curve i — 2. With a commutator such as shown 
in figure 5, and with the brushes placed as shown, it 
will be seen that just as the current in the coil is at zero 
the commutator has moved in such a position that the 
brushes are just changing from one segment of the com- 
mutator to the other, thus keeping the rising side of the 
loop connected to the negative brush and the down- 
ward moving side of the loop connected to the positive 
brush. In this way we can send all the impulses or 
waves of current from the revolving coil on the circuit 
in one direction, thus producing a pulsating current, but 
at the same time one whose flow is always in one direc- 
tion, The current curve of such a dynamo will now be 



26 THEORY O^ DYNAMOS. 

such as shown in figure 7, in which it will be noticed all 
of the waves of current are above the zero line A — B. 
This type of current is known as a direct current of pul- 
sating character. As before stated the generator, or dy- 
namo just spoken of, is of the simplest possible form and 
to make large dynamos for supplying continuous direct 
current in an economical manner such a primitive dyna- 




FIGURE 7. — PUI^ATING DIRECT CURRENT WAVE — 
SINGLE coil. ARJVIATURE. 

mo as shown, must be greatly improved. In chapter i, 
we have spoken of electro-magnets as being the only 
practical form for large and powerful magnets, and we 
will find that all field magnets for large dynamos are of 
this type. 

The armatures of large dynamos, instead of having but 
a single coil, will often have 100 or more coils, each con- 
sisting of one or more turns, for if a single turn coil will 
generate, for instance, i volt, when cutting the magnetic 
lines at a given rate, a coil of 10 turns of wire in it will 
generate 10 times the pressure that the i turn will, or 10 
volts. And as has been explained, if a piece of iron be 
placed in a magnetic field, a large number of the lines of 



THEORY OF DYNAMOS. 



27 



r^-^ 




--B 



FIGURE) 8. 



•FIvOW OF MAGNETISM THROUGH A RING 
ARMATURE CORE. 




FIGURE 9.— FivOW OF MAGNETISM THROUGH A DRUM 
ARMATURE CORE. 



^g THEORY OF DYNAMOS. 

magnetism will take to the iron in completing their in- 
dividual circuits, and so it has been found advisable to 
wind armature coils on an iron core, so that the largest 
possible number of lines of magnetism flowing from the 
poles of the field magnets, will flow through the iron ar- 
mature cores, and in this way, the coils of the armature 
will cut a larger portion of the lines given out by the 
field magnets. 

The reader will easily understand, from the previous 
description, that the current given out from a single coil 
armature may be a direct current, but still of a pulsating 
type, there being in the cases shown, two impulses in 
each revolution. 

There are many cases where such a pulsating current 
wou'd be nearly as objectionable as an alternating cur- 
rent. To overcome this trouble and to also make a dyna- 
mo whose efficiency is high enough for practical work, 
has taken an immense amount of study. To make the 
principal used to obtain a continuous current, very 
clear to the reader, it will be well to take up the case of 
a * 'ring' ' armature on which a single coil is wound. 

From figure 8 and 9, it will be seen that nearly all the 
lines of magnetism shown between the pole pieces take 
the iron path in preference to the air. In the case 
of the iron ring shown between the pole pieces, N and S, 
the lines practically divide on the line A — B half taking 
their path by way of the upper half of the ring, and the 
remaining half through the lower portion of the ring. 
Thus with a coil placed as in figure 10, it is evident that 
practically only the wire on the outer face of the ring 
will be cutting the lines of magnetism as they pass from 
the pole pieces to the ring. The coil will generate a 



THEORY OF DYNAMOS. 



29 



current while revolving from C to D, the line C— D 
being the neutral line, or line of commutation, which is 
the point at which the current will reverse its direction 
in the moving coil. This is the simplest form of ring 
armature, a step in advance is the adding of a coil 




FIGURE 10.— RING ARMATURE OF ONE COII 

on the opposite side of the ring, and connecting ttirrc in 
multiple, that is, the current generated by one. coll nas 
added to it the current of the other coil, whicn adds 
whatever current it may be generating, to that of the 
original coil. In this case, the amounts generated in 



30 THKORY OF DYNAMOS. 

two coils will be equal, for when the coil on one side of 
the ring is generating current, the coil diametrically op- 
posite must also be generating a like amount, and when 
connected in multiple as shown the total result at the 
brushes will be the sum of the two efifects. See figure 
II. It will be evident also, that while the coils are 




I^IGURK II. — RING ARMATURE. — TWO :OII.S 
IN MUI.TIPI.E. 

moving past the line C-D, fig. 8, they generate no current, 
since they cut practically no lines of magnetism, and 
that if two coils were placed on the ring so as to be 
moving past the line, A — B, they would be generating a 
maximum amount of current. By connecting these four 



THEORY OF DYNAMOS. 31 

coils as shown in figure 12, we will generate a current 
having twice as many impulses as in the case of an arma- 
ture having but one pair of coils in series. The current 
wave will be represented by figure 13. The line i — 2 
representing one revolution. 




FIGURE 12.— GRAMME RING ARMATURE. 
FOUR coil. TYPE. 

This multipljdng of coils can be carried on with econ- 
omy, until we have some dynamos of this type, having 
hundreds of coils, and giving practically a perfectly con- 
tinuous current. 

The proper placing of the armature coils in the mag- 
nelic field between the pole pieces of the field magnets. 



ja THEORY OF DYNAMOS. 

has taken an immense amount of study and experiment, 
and we to-day have two general types of armature, the 
drum and the ring type. The drum armatures are so 
called from their shape. A cylindrical piece of iron with 
the armature shaft running through its length from end 
to end. is covered with coils of wire, which in dynamos 




FIGURE 13. — CURRENT WAVES OF FOUR COII* 
RING ARMATURE. 



having but two field magnet poles, are so wound as to 
form loops similar to that shown in figure 5. This type 
of armature, with many coils each of several turns, is the 
type usually used for incandescent lighting and power 
work by direct currents. The drum armature is sometimes 
called Siemens armature, from its inventor. Dynamos having 
ring armatures have been used to a great extent for arc 
light work and are certainly a very much easier armature 
to repair than drum armatures, whose windings usually 
cross and overlap at the ends of the iron armature cores, 
and thus increase the liability to make trouble from 



THEORY OF DYNAMOS. 



33 



short circuits etc., at these points, which often make it 
necessary to remove nearly all the armature windings to 
repair the damaged coil. Ring armatures or Gramme 
armatures as they are often called, may be repaired 
quickly by removing the defective coil from the ring, 
and rewinding with a new coil, or in many cases of 




FIGURE 14. — OPEN COIL RING ARMATURE. 

trouble, the damaged coil may be disconnected from the 
commutator bars, and the two bars to which the coil was 
connected are then connected by a short piece of wire, 
and the dynamo will then be able to generate current until 
repairs are made. 



34 THEORY OF DYNAMOS 

The first arc light dynamos, the Brush and Thompson- 
Houston makes, have armatures of the ring form, but 
owing to the peculiar windings on them, cannot be called 
Gramme armatures. They are known as "open coil'' 
armatures, while all Gramme ring and drum armatures 
are known as "closed coil". This distinction is brought 
about from the fact that drum and ring armatures are, 
as has been shown, connected between windings or seg- 
ments, of commutator, in such a way as to leave the 
armature windings always connected in a permanent way 
from coil to coil, whereas in open coil armatures as 
shown in figure 12, it will be seen that the coils are sep- 
arate and distinct from each other. 

In both the Brush and Thomson-Houston dynamos, 
the armature coils are provided with terminals which 
alter the connections in such a manner as to let the coils 
in the most active positions give the bulk of the current, 
and either cut out the less active coils entirely, as in 
Brush dynamos, or reduce the resistance of such coils to 
the flow of current by placing them in parallel or multi- 
ple arc, and then in series with the active coil or coils. 

The current from both of the dynamos mentioned, is 
extremely pulsating, compared to current from the usual 
ring armature, but owing to the well worked out details 
of construction, insulation, regulation, and to the relia- 
bility derived therefrom, both Brush and Thomson- 
Houston arc dynamos are known the world over. Chas. F, 
Brush, of Cleveland, Ohio, was the pioneer in arc lighting 
work as the world now knows it, and Profs. Elihu Thomsom 
and Edw. J, Houston were not far behind him in pioneer work. 



THEORY O"^ DYNAMOS. 



3S 




FIGURE 15 — SEPARATKlyY EXCITED DYNAMO. 

We have taken up the fundamental study of armatures 
and have spoken of electro-magnets for field magnets, 
and the various methods in vogue for energizing them 
will now be taken up. It takes a current of electricity, 
passing around an iron core or center to make an electro 
magnet, the power of which will vary with the ampere 



36 



THEORY OF DYNAMOS. 



turns, or the product of the number of amperes passing 
and the number of turns of wire around the iron core. 
The first dynamos built with electro magnets for field 
magnets were * 'separately excited, ' ' that is, had a separ- 
ate battery or generator of electricity to furnish current 




FIGURE 1 6. — SERIES WOUND DYNAMO. 

to energize them, the plan of connections being shown in 
figure 15. Then it was seen that the current from the 
dynamo itself might be used to excite its own field mag- 
nets and owing to a slight amount of "residual magnet- 
ism", which always remains in a piece of iron after hav- 
ing once been magnetized, being present in the field 



THEORY OT? DYNAMOS. 



37 



magnets, this was easily accomplished, as shown in 
figure i6, and is known as a ''series winding" and such 
a dynamo would be known as a "series wound" dynamo. 
The field winding carries the whole current of the arma- 
ture and is connected in series with it. This winding is 




FIGURE 17.— SHUNT WOUND DYNAMO. 



generally used in arc light dynamos, and others gener- 
ating a constant current of high voltage. 

The plan of a shunt winding is shown in figure 17, 
and is so called from the fact that the winding forms a 
"shunt" path around the armature. To make an effici- 
ent dynamo, the resistance of the shunt winding is made 



38 THEORY OF DYNAMOS. 

quite high, several hundred times the resistance of the 
armature and as a result, the current through the shunt 
is small in quantity, but the immense number of turns of 
small size wire in the coils on the field magnets make 
the necessary number of ampere turns, and thus the 
resultant magnetism is the same as that produced in the 
series dynamo with its large current and small number 
of turns. Shunt wound dynamos are usually used to 
generate currents of * 'constant potential" or * 'constant 
voltage' ' such as is used in operating incandescent lamps, 
electric motors, etc. Owing to the high cost of wire 
necessary for shunt windings for dynamos of high volt- 
age, we will find that practically all shunt dynamos oper- 
ate at a voltage under 600, in fact, by far the largest 
number of shunt dynamos operate at a voltage of not 
over 125 volts. For regulating purposes a rheostat (R) 
containing resistance wire, is placed in the shunt circuit, 
and in this way a practically uniform voltage is main- 
tained at all loads by varying the total resistance of the 
shunt circuit, and thus the current through it, which 
must in turn vary the magnetism of the field and in this 
way raise or lower the voltage, as the case may require. 

Still another winding is shown in figure 18, known as 
the* compound winding, and is often used to make a dy- 
namo self-regulating It is evident, that on a constant 
potential circuit when additional lamps are turned on, 
that the dynamo must respond at once and send out a 
larger number of amperes to take care of the load. 
Under these conditions, to maintain the voltage constant, 
we must increase the magnetism of the field magnets to 
compensate for the increased output. This may be ac- 
complished in an automatic manner by winding a large 



THEORY OF DYNAMOS, 



39 



portion of the field with a shunt winding, which should 
be of such strength as to generate the rated voltage of the 
dynamo when there is no load placed on it. Then the 
series windings must be sufficient to add enough ampere 
turns as the load rises, to keep the voltage up to standard 
or in some "over compounded" dynamos to increase the 




FIGURE l8. — COMPOUND WOUND DYNAMO. 

voltage slightly as the load increases, so as to compensate 
for loss in line or feeders supplying lamps, etc. This type 
of dynamo is largely used in lighting plants having a 
fluctuating load, and is invariably the type used to gen- 
erate current for street railway work, where the load is 
an ever varying quantity, a condition under which the 



40 . THEORY OF DYNAMOS. 

compound wound dynamo is practically the only one 
which gives satisfaction. 

There are a number of modifications of these principal 
windings which are seldom run across and for this reason 
are not explained in detail; suffice to say, that dynamos 
can be, and have been made, which, by means of the prin- 
ciples described, will give a constant current and varying 
voltage, a constant voltage and a varying current, in both 
cases the speed being maintained uniform, or as in some 
cases of dynamos designed to be connected to the axle of 
a car for train lighting, the voltage remains practically 
uniform, with a varying current, while the speed alters 
several hundred per cent. 

It will be seen that we have various types of armatures 
and field magnets with their various windings, and it 
will be be easy to see that it is possible to build dynamos 
of almost any size, and for any kind or character of 
current. 



CURRENT DISTRIBUTION. 4I 



CHAPTER IV. 



curre:nt distribution. 



In the previous chapters, we have treated of direct and 
alternating current dynamos, and to a certain extent, 
their application. In this chapter we take up the meth- 
ods of distributing current to lamps, motors, etc., all of 
which are deseiving of much study. 

The dynamo for lighting or power purposes, usually 
sends current a considerable distance before it is used in 
the arc or incandescent lamps, motors, etc. 

It is evident that it is desirable to have as little loss as 
possible in power, between the dynamo or generator and 
the point at which the current is used. 

For this reason, conductors of copper are used, owing 
to its ^^conductivity," that is, its small resistance to the 
flow of current. But even in the purest copper, there is 
some resistance, the amount varying with the length, 
and also with the diameter or * 'cross-section" of the cop- 
per. If we attempt to reduce the loss to a very, small 
amount, the cost of copper will be high and if there is 
not enough copper, the loss in pressure will be excessive. 

To prevent a loss of current from the conductors, from 
them accidentally coming in contact with the ground or 
other conductors of electricity, the wires are insulated 
from each other and from all connections to the ground. 
In high potential work, this insulating of conductors 



42 CURRENT DISTRIBUTION. 

would have to be done for safety to human life, for pres- 
sure of 600 volts and over are exceedingly dangerous. 

The distribution of current for series arc lighting is a 
simple matter, since the current in amperes is constant 
and uniform in all parts of the circuit and the loss in one 
portion of the wire circuit will be the same as in any 
similar length of the same size wire. Thus in calculat- 
ing losses in the wiring leading to arc lamps in series 
circuits, the main thing to determine is the total resis- 
tance of the wire, and, having the resistance in ohms, we 
easily calculate the number of volts lost in passing the 
6, 8 or 10 amperes, as the case may be, through the wire. 
The loss in volts will be the number of amperes, multi- 
plied by the number of ohms or, expressed in symbols of 
ohms law, K=CxR. 

Thus, on an arc light circuit 10 miles long, consisting 
of No. 6 B & S Guage Wire, which we may see from con- 
sulting the wire table in the back of book, has a resis- 
tance of practically, 2 ohms per mile (2.088) that with 
10 amperes of current flowing, that the loss in volts, per 
mile, will be 10X2 or 20 volts, 10 miles would thus be 
200 volts, which is the pressure required to force the cur- 
rent through ths wire circuit, this being independent of 
the number of arc lamps in series, each one of which 
adds from 45 to 50 volts to the 200. Thus a circuit, 10 
miles long, of No. 6 wire and 50 — 50 volt lamps connected 
in series on it, will take a total electro-motive force in 
volts of 200 (line resistance) -\- 2500, which is the total 
voltage required for the lamps themselves (50X50) which 
makes a total of 2700 volts required to force 10 amperes 
tnrough the circuit with its lamps. The loss in volts 
bein^ 200, and the total voltage necessary to operate the 



CURRKNl* DISTRIBUTION. 43 

lamps on such a circuit, being 2700, it is evident that the 
per cent, of loss on such a circuit will be Voo*» or nearly 
7X%j which in practice would not be considered exces- 
sive. If No. 4 B and S wire were used in place of No. 6, 
'he loss would have been only 130 volts or 5% loss, but 
the extra cost of copper wire provided with a good rub- 
ber insulation, would have been nearly $800 over a No. 6 
wire and the extra loss in current is not enough to pay 
for putting up a No. 4 wire. Smaller wire than No. 6 
can hardly be recommended, however, on account of the 
increased trouble in keeping up a long line of small wire 
which is likely to be broken easily by sleet, wind, etc. 

Incandescent lamps are sometimes connected in series 
in the same manner as arc lamps; but the current will 
usually be found to be less than 5 amperes, although 
there are some series incandescent lamps made to run on 
10 ampere ci/cuits in series with arc lamps. Owing to 
the danger co::iriected with the handling of such scries 
incandescent lamps, due to the high voltage on which they 
usually operate, they are not in very general use and are 
being discarded more and more each year for indoor 
illumination. 

It will be seen that in any series circuit that if the cir- 
cuit be broken at any point that it will stop the flow of 
current through all the lamps connected and for this 
reason all arc and incandescent lamps designed for series 
work are provided with **cut out" which preserves the 
circuit in case of trouble with an individual lamp, so as 
to allow the remaining lamps to operate. In arc lamps 
on series circuits, the cut out ''short circuits," the lamp 
in case of the carbon being consumed or broken or in 
case of a carbon rod in the lamp, sticking or * 'hanging 



44 CURRENT DISTRIBUTION. 

Up." In the case of incandescent circuits, there is usu- 
ally provided a socket for the lamp in which is a cut out, 
designed to preserve the continuity of the circuit in case 
from a lamp being broken or removed from its socket. 
Arc lamps for series circuits are nearly always operated 
on direct current dynamos. However the arc lamp is being 
adapted to the alternating current more and more and wil 
probably replace the greater part of direct current arc service. 

The second and without doubt the most generally used 
plan of current distribution for either power or illumin- 
ating purposes, is that by means of the constant poten- 
tial dynamo and a multiple or multiple series system of 
distribution. Practically, all incandescent lighting, all 
distribution of current for power purposes and quite a 
portion of recent arc lighting plants are furnished with 
current from constant potential dynamos of either alter- 
nating and direct types. 

To distribute current at a constant potential or voltage, 
great care must be exercised in designing the plan of 
wiring to be used, for it is a very necessary thing to have 
the pressure in volts as near a constant quantity as possi- 
ble. This will be found especially the case in incandes- 
cent lamp installation. A slight rise of voltage above 
that for which the lamps are designed, will decrease the 
life of the lamp to an alarming extent. A slight 
reduction in the voltage, will increase the life to a great 
extent but the light given out by the lamp will decrease 
so much as to be unsatisfactory. 

The method of calculating the size of wire for constant 
potential distribution may be easily understood after a 
study of the relation of size of wire to its resistance. A 
copper wire 98% pure, which is y^^n o^ an inch or one 



CURRENT DISTRIBUTION. 45 

circular mil. in cross section, will be found to measure 
10.355 ohms per foot of length, at a temperature of 20^ 
Centigrade or 68° Fahrenheit. Knowing the resistance 
of a wire one mil in diameter and one foot long to be 
10.355 ohms, we may then calculate the resistance of any 
wire, provided we know its length in feet and area in 
circular mils. On a foot length, a wire 2 circular mils in 
cross section will have but half the resistance of the wire 
having one circular mil area or 5.1775 ohms per foot 
length. The smallest wire usually carried in stock by 
dealers in wire for magnets, etc., is 25 C. M. in area and 
is known as a No. 36 wire and has a resistance of .4142 
ohms per foot of length or ^ as much as a wire i CM. in 
area. The smallest wire used in wiring for incandescent 
lamps and other electric light distribution (No. 16 B. & 
S.) has an area of 2583 C. M. and a resistance at 68° Fah- 
renheit of .004009 ohms per foot of length. A No. 6 B. & S. 
copper wire which has been spoken of as a very largely 
used size for distribution of arc light current on series 
circuits, has an area of 26,250 C. M. and a resistance of 
.0003944 ohms per foot. The temperature of the wire 
has an effect on the resistance of the metal of which it is 
made. Copper wire increases its resistance as the tem- 
perature rises, but for ordinary conditions the rise is so 
slight that it need not be considered. Knowing the 
resistance of a certain size wire in ohms per unit length 
and the distance to lamps or motors from the source of 
current, we may easily calculate the loss or drop in volts 
with a given current in amperes passing, by means of the 
equation, V=CXR, or, the volts lost will equal the num- 
ber of amperes multiplied by the total resistance, ex- 
pressed in ohms, of the copper wire. It must be remem- 



46 CURRENT DISTRIBUTION. 

bered that we must look at the loss in the -v/iring as a 
distinct and separate expenditure of power, which is 
entirely independent of that taken by lamps, motors, etc 
to which the wiring conveys current. 

We have shown how the loss in volts may be calcu- 
lated, provided w^e know the total resistance of the con- 
ducting: wires and the current passing through them. 
The condition most usually encountered is that where 
the maximum number of volts available to overcome con- 
ductor resistance is known, and also the distance to the 
lamps from the source of supply. The unknown quan- 
tity is the area or size of the wire necessary to carry the 
amount of current needed at lamps, etc., with the loss 
in volts decided on. 

On electric light plants, for example, where i lo volt 
incandescent lamps are used, we will find that the volt- 
age, at the dynamo, will probably be from 115 to 125 
volts, depending on the distance from the dynamo to the 
lamps, the difference between 1 10 volts and the voltage 
found at the dynamos, being the number of volts used to 
overcome the resistance of the conducting wires. Dyna- 
mos for supplying direct current for constant potential 
work are usually shunt or compound wound and by 
means of a rheostat in series with the field magnet cir- 
cuit, can have their voltage raised as the load increases, 
so as to maintain a uniform voltage at the lamps. This 
energy or power lost, shows itself in heating the copper 
conductors and of course is a loss which must be made 
as low as possible without an excessive outlay for copper 
wire. The loss in watts in a given conductor varies with 
the square of the number of amperes passing through it 
Thus, in a conductor having i ohm resistance, 10 volts 



CURRENT DISTRIBUTION. 47 

will pass lo amperes. The loss in watts being the pro- 
duct of the number of volts and amperes, loXio or loo, 
which is the number of watts used in such a conductor 
when lo amperes are passing. If 20 amperes were then 
passed through the same conductor we w^ould find that it 
took 20 volts pressure to put it through. The watts used 
being now 20X20 or 400, or 4 times the power that 10 
amperes required. 

It has been mentioned that this loss shows itself by 
heating the conductors and in this connection it must be 
stated that but a slight rise in temperature can be 
allowed, on account of the danger from fire at points in 
buildings where the conductors pass near wood etc. If 
a conductor is enclosed in an insulating covering, its 
radiating capacity is reduced, for as a general thing, in- 
sulators are poor conductors of heat. Thus, after a great 
deal of experimenting under various conditions, a table 
was made, showing the * 'safe carrying capacity' ' of copper 
wires of various sizes, (see table in back of book). The 
carrying capacity given in this table is that allowed by 
the Board of Underwriters for wires used for interior 
work. 

We can see that there are two limits between which we 
must work. The wires must not be allowed to carry 
more than their safe carrying capacity, in which case 
we will probably find that the per cent, of loss would be 
higher than it should be, nor can we increase the size of 
our conducting wires to any great extent over that abso- 
lutely necessary, without making the cost of copper 
excessive. 

The fundamental elements of the case now having 
been explained, let a practical case be taken. I^et the 



48 



CURRENT DISTRIBUTION, 



dynamo D, figure 19, designed to furnish a constant 
potential current, be connected by wires to 100 incandes 
cent lamps in each of two buildings, 1000 feet distant* 
The incandescent lamps are to be made to give 16 c. p at 
JIG volts pressure. The wires from the dynamo to the 
* 'centre of distribution" will be called ''feeders". The 
centre of distribution being the point at which the feed- 
ers are connected to the ' 'mains. ' ^ 



T 



feedtt'i 






iOr«, Vi^'CAt**"- 




n«!i»"A« 






FIGURE 19. — PI.AN OF CURRENT DISTRIBUTION SHOWING 
FEEDERS, MAINS AND PRESSURE WIRES. 



When the buildings are reached, the wiring then con- 
sists of "mains" and the service wires, or tap circuits 
from the mains on which the incandescent lamps are 
placed. Thus the distributing system of such an incan- 



CURRENT DISTRIBUTION. 49 

descent light plant will consist of feeders, mains and the 
branch circuits to the lamps to the mains. The aim will 
be to keep the voltage at the mains, constant and uni- 
form, the pressure in this case being about 112 volts, and 
thus allowing for about 2 volts loss at full load, between 
the mains and the lamps themselves. The dynamo will 
generate a maximum of 125 volts, thus giving a maxi- 
mum voltage to be used in overcoming the resistance of 
the ''feeders" at full load, the difference between 112 
and 125 or about 13 volts, which is about 10% of 125 
volts. To show the pressure of the mains which we have 
shown have a voltage but slightly higher than that used 
by the lamps, "pressure wires" are usually run back 
from the mains to ''pressure indicators" or voltmeters 
situated in the dynamo room. Thus at a glance, the 
dynamo tender can see the exact voltage at the lamps 
and regulates his dynamo accordingly. 

Assuming that this is a practical case, we first desire 
to know what the size of the wire must be for the feeders 
to carry current for the 200 lamps with a loss of 13 volts 
or 10% in the wire. The 16 candle power lamps of no 
volt type, will take practically ^ ampere each. Thus, 
the dynamos will have to supply 100 amperes for the 
200 lamps. 

The formula for calculating the size of the feeder, is 

21.21 C D 

C. M. = — 

K 
C. M.=Area in Circular Mils. 

2i.2i=Resistance of 2 feet of copper i mil in diameter. 
C=Current in amperes. 
D=Distance in feet, to the lamps. 



50 CURRENT DISTRIBUTION. 

K=Loss in volts in the wire. 

In the case given, C=ioo, D=iooo and E=I3. 

Thus the size of the wire in circular mils or C. M. is 

2 1. 21X100X1000 

=163, 153 

13 
Thus the wire must have a sectional area of 163,153 cir- 
cular mils to carry the 100 amperes, 1000 feet, with a loss 
pressure of 13 volts. By consulting the table of wire in 
sizes in the back of the book, it will be seen that the 
nearest size, is No. 000 B. & S., which has an area of 
167,800 C. M. The diameter in mils or thousandths of 
an inch of such a wire is 409.6. Thus it is seen that to 
maintain a pressure of 112 volts at the buildings 1000 feet 
from the dynamo, when the 200 lamps are burning, will 
require a No. 000 B. & S. wire. 

We have shown the buildings i and 2 to be 200 feet 
apart, and as before stated, it is desirable to make the 
loss in the mains as low as possible; in this case for ex- 
ample, I volt. What size wire must be used ? We will 
use the formula used in the first case, 

21.21 CD 

C. M. = 

E 
there will be a current of 50 amperes in either branch 
from the centre of distribution to the buildings. Thus 
in the formula, C=5o amperes, D=ioo feet and B=i 
foot, thus: 

21.21X50X100 

^=C. M. or 106,050 

I 
which is slightly larger than a No. o B. S. wire, 
which has an area of 105,592 C. M. We now have our 



CURRENT DISTRIBUTION. 5I 

wire sizes to deliver current inside the buildings at iii 
volts, which leaves one volt to be expended in overcom- 
ing the resistance of the service wires, from the mains to 
the lamps themselves. This loss is calculated in the 
same manner as the other two cases. We may in this 
calculate the size wire necessary to deliver any number 
amperes any distance at any loss and the formula should 
be remembered by anyone having any distributing work 
to do, as it makes him entirely independent of wiring 
tables, since he has the key to the whole plan himself. 

In all constant potential distributions, safety devices 
must be so placed in the conducting wires, as to make it 
impossible to overload the dynamo or wiring by an extra 
flow of current, due to metallic contact between the 
wires, accidentally or otherwise and thus produce what 
is known as a "short circuit". Short circuits may be 
caused by two wires having a difference of pressure com- 
ing in contact with each other or with any other con- 
ductor, so as to cause an excessive flow of current which 
may overload the dynamos or perhaps melt the conduct- 
ing wires unless a safety device is so placed as to 
cut off" the current until the trouble is remedied. On the 
usual constant potential circuits used for lighting "fuses", 
made of an alloy having a low melting point, are placed 
in the circuit, so as to melt when an excessive amount of 
current pass through them and thus open the circuit. 
In figure 19, fuses at A. B. and C. are so placed as to pro- 
tect the wiring, as shown. The fuses at A. would be of 
such size, as would carry 100 amperes safely, but any 
excessive amount above this, would speedily heat 
the fuses to their melting point and the circuit 
would then be "open". At B and C the fuses would be 



52 CURRENT DISTRIBUTION. 

of 50 amperes carrying capacity and any rise above 50 
amperes would melt the fuse and protect the wiring be- 
yond it. It should be understood that fuses are used 
simply to prevent more current to pass through a wire 
than its safe carrying capacity allows, and whenever 
placed should be so arranged as to size as to open the 
circuit before the wire is carrying more than its safe^ 
carrying capacity. They must melt before the smallest 
wire which they protect, shall have passing through it 
more current than the law allows. Fuses even at theii 
best, are often sluggish in operating, especially when of 
large size, and great care must alv/ays be exercised in 
putting the proper fuse in the proper place. 

For places where an unusually heavy fuse would have 
to be placed, such as the dynamo room of a street rail- 
way plant, instead of fuses, "circuit breakers" are often 
placed, which open the circuit by mechanical means and 
they are undoubtedly far more reliable and satisfactory 
than any system fuses could be. The usual plan of oper- 
ating mechanical circuit breakers, is to have a magnet 
carrying the whole current of the wire it protects, so 
arranged as to trip a catch when the maximum current 
is reached, and this catch releases the contacts, which 
separate and thus open the circuit. 

The loss of electrical energy in a conductor of a given 
resistance varies with the square of the current in am- 
peres passing through it. If a certain wire has for in- 
stance, 5 ohms resistance, it will take 10 volts pressure 
to put 2 amperes through it, the loss in watts being 2X10 
or 20. If we pass 4 amperes through this same wire it 
will take 20 volts, the watts being now 4X20 or 80, thus 
in doubling the current in a given wire, the loss in watts 



CURRENT DISTRIBUTION. 53 

will be increased 4 times or as before stated, it varies 
with the square of the current. 

For the reason that the loss in a conductor varies with 
the square of the current in amperes passing through it, 
it has always been the aim of electrical engineers and 
inventors to make lamps, motors, etc. , operate at as high 
a voltage as is permissable with due regard to safety and 
reliability. Up to the present time incandescent lamps 







um 




G FIGURE 20.— SIMPIvE MUI.TIPI,E SYSTEM, DYNAMO 
SUPPI^YING 10 I.AMPS. 

have not been made so as to give good results at any 
higher voltage than about 1 10 volts and for this reason 
we are practically limited to no volts pressure as the 
highest to be used for the operating of incandescent 
lamps when placed in multiple. 

The Edison 3 wire system was designed to make it 
possible to carry current a much greater distance from 
the dynamo than was possible by the simple multiple sys- 
tem without great loss, and by its use the loss can be 
greatly reduced in a system of distributing current for 
lighting. The amounts of copper necessary to distribute 
current for a certain number of lamps, by the 3 wire sys- 
tem is about ^ of that used in the simple multiple 
system. 

The explanation of the plan of wiring will be shown in 



54 



CURRENT DISTRIBUTION. 



the figures 20, 21, 22 and 23. In Fig. 20, the no volt 
dynamo D, is shown connected to its load of 10 incandes- 
cent lamps. The current flows out from the positive 
brush and then through the lamps back to the negative 




FIGURE 21 — TWO DYNAMOS SUPPIyYING 5 I.AMPS EACH, 
ON MUI.TIPI,E SYSTEM. 





6 



6000 



FIGURE 22. — MUIvTlPLE SERIES SYSTEM FOR lO LAMPS. 



brush; assuming that each lamp is 32 candle power at 
no volts pressure, it will take one ampere of current, 
thus the 10 lamps take 10 amperes of current. This plan 



CURRENT DISTRIBUTION. 



55 



as shown in Fig. 20 is a simple multiple plan of wiring 
Fig. 21 shows the same number of lamps but they are 
supplied by two dynamos Di, D2, each of half the 
capacity in amperes but the same voltage as dynamoD in 
Fig. 20. Thus with the 5 lamps connected to each 
dynamo, there will be 5 amperes flowing out from the 
positive brush and through the lamps back to the 
negative brush of each dynamo. Now, if the two 
dynamos Di and D2, were connected in series and each 
of them was designed to generate 1 10 volts it is evident 




6UTI 



Jit^H? 



FIGURE 23. — EDISON 3 WIRE SYSTEM SUPPI^YING 
10 I.AMPS. 



that the 1 10 volt lamps may be connected in series of two 
and give their proper candle power as shown in Fig. 22. 
The current flowing out from the positive brush of Di 
will be but 5 amperes, for there are now 5 series of 2 
lamps each, each series taking i ampere at 220 volts 
pressure. 

This plan would not meet practical conditions, for if 
one lamp of a series of two were turned out, its mate 



56 CURRENT DISTRIBUTION. 

would al^o be extinguished. A single lamp could not be 
turped on and oflf at will and to make it possible to do so, 
a tnird wire must be added, Fig. 23, which will make it 
an icdison 3 wire system. In this case D-|- and D — repre- 
sent the dynamos Di and D2 in figure 21 & 22. The 3 
wires are marked -J-, + and — , and are called respec- 
tively, positive, neutral and negative wires. The two 
dynamos are connected in series as in figure 22, and the 
pressure between the* two outside wires -f- and — , is 
therefore 220 volts. The pressure of each dynamo being 
I ID volts, there must be but 1 10 volts pressure between 
the -{- and the +, or between the + and — wires. The 
current flowing out from the -\- brush of the dynamo D-|- 
must be but 5 amperes and as long as the loads in am- 
peres are equal on both * 'sides' ' of the system there will 
be no current flowing in or out on the middle or ± wire. 
If, however, a lamp is turned off" on the ''positive side" 
of the system, (the lamps supplied by D+) the current 
flowing out on the + wire will be but 4 amperes, which 
will destroy the balance and we will then find a current 
of one ampere flowing out on the neutral wire to make 
up the 5 amperes needed for the "negative side" of the 
system. The current flowing on the neutral wire will be 
the difference between the loads in amperes on the two 
sides of the 3 wire system. If the loads in amperes on 
the two sides balance, the station switch on the neutral 
wire can be opened and the lamps will not be affected. 
With the neutral switch closed, it is evident that by 
opening station switch on the positive wire, that all the 
lamps on the -\- side will be put out, but that the lamps 
on the — side will burn as usual and if the station switch 
on the negative wire is opened and the positive and neu- 



CURRKNT DISTRIBUTION. 57 

tral switches closed, the + side will burn and the — side 
be put out. 

As to the saving in copper and relative losses in this 
system as compared to the simple multiple system, it 
will be noticed that the outside wires carry but half the 
number of amperes that would be necessary on the mul- 
tiple system, figure 20, and that the middle or neutral 
wire usually carries but a small amount as compared to 
the outside wires. Thus, if for a moment we ignore the 
necessity for a neutral wire, the size necessary for the 2 
outside wires will be found to be but % the size necessary 
to supply current for the same number of lamps, the 
same distance from the dynamos, in a simple multiple 
system of distribution, for the current at 220 volts is but 
5 amperes, and the loss is twice as many volts, for if we 
assume a loss of 2 volts from the dynamo to lamps on the 
simple multiple system, the dynamo voltage must be 112 
volts and the voltage at the lamp is 1 10. Thus in the 3 
wire system with each dynamo generating 112 volts, we 
will have 224 volts between the outside wires at the dyna- 
mo and since the two 1 10 volt lamps in series need but 
220 volts, it will be seen that we can allow a 4 volt loss in 
our wiring and still have the lamps up to candle power. 
Thus it will be seen that our loss in volts is 4 instead of 2 
and our current in amperes is reduced from 10 to 5, thus, 
each of our outside wires need but be % the size that 
would be necessary for the same number of lamps on a 
simple multiple distribution. 

As has been stated the middle or neutral wire should 
carry but a very small amount of current in a well de- 
signed 3 wire system, but for the reason that the fuses on 
either of the outside wires might be melted in case of a 



58 CURRENT DISTRIBUTION. 

short circuit and thus make the middle wire carry as 
much as the outside wire, the rule has been followed, of 
making the neutral or middle wire as large as either of 
the inside wires, thus we have 3 wires, each X ^^^ ^^^^ 
that would have been necessary for each wire of a simple 
multiple system and the relative amounts of copper will 
thus be 3XX=^ ^^^ 3 wire or 2X1=2, the size for sim- 
ple multiple wiring, the relations are thus : ^ to 2 or 
^ to I. 

In calculating wiring for 3 wire distributions we may 
get the size necessary for a simple multiple system of 
wiring for the number of lamps we desire to run on the 
3 wire system and then divide the area of the wire in cir- 
cular mils needed for each of the wires of the multiple 
system by 4, which will give the area of the size wires 
needed to distribute current to the same number of lamps 
by means of the 3 wire system. 

The Bdison 3 wire system is used by nearly all the 
larger size stations supplying direct current for incan- 
descent lighting. 

There are 4 and 5 wire systems sometimes used, which 
are operated on the same plan as 3 wire systems with the 
exception that an extra dynamo is used for each addi- 
tional wire, thus a 5 wire system will have 4 dynamos, or 
their equivalent, all working on the same lighting sys- 
tem. It is doubtful if the extra complication necessary 
with such a system is in the line of economy or not, es- 
pecially with medium sized plants. . 

For supplying current to street car motors, a plan of 
current distribution is used, which in the usual single 
trolley systems is very different from that used to supply 
current for illumination. 



CURREN'C DISTRIBUTION. 



59 



The usual method employed will be readily understood 
from figure 24. The dynamo D of the compound wound 
constant potential t3'pe is designed to generate a varying 
amount of current at about 500 volts pressure. The pos- 
itive brush is connected to the trolley line L and the 
negative brush should be connected to the rail or to the 
copper wires laid in the ground near the track, which 
serve as the return circuit for the current. Thus the neg- 
ative side is always * 'grounded" and in fact, the earth 
itself is used to a limited extent for the return circuit of 
the current used in operating the motors on the cars. In 
most cases it has been found that the earth cannot be 



*;:S2' 




Q Q']'St 



i_A^, ajfi^j, . ,[i^^ 



=5^ 



f^erui'y C" 



l^IGURK 24 — STREET RAII^WAY TROI,I,EY SYSTEM. 



depended on to furnish a path of low enough resistance 
to insure satisfactory results and a system of * 'bonding' * 
is always resorted to. The ''bonding" consists of uniting 
the ends of the rails together by means of heavy copper 
"bond wire" thus making use of the metal section of the 
rail to form a continuous metallic circuit from the cars 
back to the power house. The question of a good return 
circuit that is durable, is one that has worried the de- 



6o CURRENT DISTRIBUTIQN. 

signers of electric street railways a great deal. This is 
owing to electrolytic action on the rails, bond wires or 
on water and gas pipes or other metal conductors near 
the line of electric road. If a current of electricity be 
made to flow from or to a metal plate immersed in a con- 
ducting fluid, an electro-chemical action is set up which 
disintegrates or destroys the metal, the rate depending 
on the amount of current flowing. This same action is 
taking place on the rgiils and other metal conductors 
when they are placed in moist earth, and its destructive 
action will depend on the amount of current flowing 
from the metal to the earth. In an electric street railway 
track, if the rail circuit contains considerable resistance, 
part of the current will flow to the earth from the rail, 
and if water pipes or other good electrical conductors in 
the earth are in such a position as to make a part of the 
return circuit, current will be conducted through them, 
and the chemical action set upon the metal surfaces will 
rapidly destroy them and make great trouble. The only 
way to obviate this trouble is to make the return circuit 
through the track so good that there will be but little 
current flowing from the rail to the ground, for the cur- 
rent will always divide depending on the relative resist- 
ance of the paths offered it. 

There are some cases of distribution of street railway 
current by means of two trolley wires, one of which is 
connected to the positive brush and the other to the neg- 
ative. In this case the earth and rails do not form a 
return circuit, the entire distribution being effected by 
means of the two trolley wires, between which 500 volts 
pressure is maintained. The motors are of course con- 
nected between the two wires, by means of two trolleys, 



CURRENT DISTRIBUTION. 6l 

which bear against the trolley wires and thus make con- 
tact with them. 

Underground conduit distribution for street railways is 
gradually being developed, and in some cases we will 
find the rail being used as a return circuit and in others 
two underground trolley wires are used, insulated from 
each other and from the earth, in which case the con- 
ducting wire of course have no more connection with the 
rail as a return circuit than the double trolley system of 
overhead distribution, does with the tracl« circuit. 



62 AWERNATING CURRENT. 



CHAPTER V. 



TRANSFORMERS AND ALTERNATING CURRENT 
DISTRIBUTION. 



In the preceding chapter, we have not spoken of alter- 
nating current distribution and have purposely avoided 
doing so for the reason that there are several peculiar 
characteristics of pulsating and alternating currents 
which should be thoroughly studied by themselves. 

By suddenly completing and then breaking an electric 
circuit, it will be found that there seems to be an action 
take place, similar to that of inertia. The current does 
not rise instantly rise to its full value and when the cir- 
cuit is broken, there will be evidence of the current tend- 
ing to resist the breaking of the circuit. This effect 
varies with the * 'inductance' ' of the circuit. The induc- 
tance being the magnetism producing effect of the circuit. 

If the circuit is through a coil wound on an iron core, 
the effect will be much greater than if the wire is not 
wound in coil form. 

This action is caused by the lines of magnetism or the 
magnetic field being generated around the wire when 
the current is started through it. Each wire has its 
magnetic influence which is created the instant that the 
current starts flowing through it. If this wire is part of 
a coil, its magnetic influence must affect other neighbor- 
ing wires of the same coil. The effect will always be 



AI^TKRNATING CURREJNT. 63 

Such as to retard the flow of current through such a coil, 
until the full current strength is reached. The ''self- 
induction'* as it is called, will vary with the square of 
the number of turns in the coil. Thus, a coil of 10 turns 
has 100 times the self induction which a coil of one turn 
would have. If, then, we connect the terminals of a 
large coil of wire which surrounds an iron core, to a 
source of electricity, we will find that it takes an appre- 
ciable time for the current to reach its full strength, and 
that when the terminals are disconnected, that a spark 
will show itself in breaking the contact which is many 
times larger than it would have been, in case the same 
amount of current was interrupted, which had not passed 
through a coil such as described. The self-induction of 
a circuit, always resists the sudden starting and stopping 
of a flow of current. This effect may be very easily dem- 
onstrated by placing an ammeter in series with a field 
magnet circuit of a shunt wound dynamo and watching 
the gradual rise in current through the circuit, on con- 
necting it to a source of electricity. On a ''dead beat" 
ammeter, that is, an ammeter whose needle comes 
instantly to the correct reading, without going past it, 
the gradual rise can be readily seen, and on breaking 
the field magnet circuit, a flash will take place which 
clearly shows that the current resists being broken. In 
fact, the voltage at the terminals of a no volt dynamo 
field coil circuit, may be several times 1 10 volts the in- 
stant the circuit is broken and a shock obtained in this 
janner is often exceedingly painful, if not dangerous. 
It will now be evident that when a current of electricity 
is started through a coil of wire, that each wire is send- 
ing out its magnetic influence, which may effect other 



64 



AIvXERNATlNG CURRENT. 



conductors in its vicinity and in fact, if two coils of wire 
are placed near each other so that the magnetic influence 
of one coil may affect the other, it will be found that the 
instant current is started in one coil that a current will 
at once be generated in the second coil, the amount gen- 
erated depending on the resistance, etc. , of the second 
coil. It will be found that the current in the second coil 



JROn CORE*. 




J) I000V0LT5. 

PRiynARV- 

COIL Of 100 



100 VOLTS, 

SECONDARY. 

COIL OF 10 



FIGURE 25. — IRON CORE WITH PRIMARY AND 
SECONDARY COII^. 



will only be generated while the current in the first coil 
is being increased or diminished and that the instant 
that the current in the first coil becomes a constant quan- 
tity that the current in the second coil falls to zero. 
Also that the current in the second coil flows in one 
direction during the rise of current in the first coil 
and that the current flows in an opposite direction 
when the current in the first coil diminishes in 



ALTERNATING CURRKlfT. ^S 

strength. Thus by sending a pulsating or alternating 
current through the first or primary coil, a pulsating or 
alternating current may be generated in a second or sec- 
ondary coily although there is absolutely no metallic 
connection between them. See figure 25. 

Alternating current dynamos are easier to build than 
pulsating direct current dynamos, and are certainly eas- 
ier to handle. They have no commutator, but instead 
have collecting rings which are the terminals of the 
coils on the armature. Brushes bear on these rings 
and in this manner connect the armature coils to the 
wiring connected to the lamps, The usual alternating 
current dynamos used for lighting purposes, give out from 
15,000 to 16,000 alternations per minute, although dyna- 
mos lately constructed are being made from 6,000 to 9,000 
alternations per minute, which is in the line of for- 
eign practice. The usual alternating current dynamo is 
designed to generate either 1,000 or 2,000 volts and a 
varying number of amperes, and this pressure is reduced 
at a transformer y to 50 or 100 volts for use in operating 
the usual incandescent lamp. 

The electro-motive force or voltage generated in the 
secondary coil, as compared to the voltage on the pri- 
mary, will depend on the relative number of turns in the 
two coils. If the primary coil is connected to 1000 volts 
pressure of alternating current and has 100 turns in it, we 
will have generated in a secondary coil of 10 turns, a 
pressure of 100 volts, or if there are but 5 turns of wire in 
the secondary coil, we will have but 50 volts between its 
ends. We can in this manner generate alternating cur- 
rents of high voltage and distribute them long distances 
from the dynamos, with a small loss and when the build- 



66 ai,te:rnating current. 

ing is reached which is to be lighted, the hiejh pressure 
current is connected to the primary coil of a transformer^ 
on the secondary coil of which the lamps are connected. 
If there is i ampere at looo volts or looo watts passed 
through the primary coil, we will find practically the 
same number of watts given out by the secondary coils, 
the only change being that at loo volts we will have a 
current of lo amperes or at 50 volts — 20 amperes. Thus 
the current in amperes is increased in proportion to the 
reduction of pressure and it is possible in this way to 
generate any voltage desired on the secondary winding, 
by proportioning the number of turns in the primary 
and secondary coils. The efficiency of transformers, that 
is, the proportion of the energy supplied the primary 
coil given out by the secondary varies in different makes, 
but at full load, large transformers can be made to give 
to the secondary from 95% to 97% of the energy supplied 
the primary. 

Figure 26, represents an alternating current dynamo, 
generating a constant pressure of 1000 volts, connected 
to 2 transformers, i of which (No. i) reduces to 100 volts, 
the proportion of turns on its primary and secondary 
coil being 10:1, and the second transformer (No. 2) reduc- 
ing to 50 volts the proportion of turns in the two coils in 
this case being 20:1. 

The same dynamo may supply a third form of trans- 
former which is called a ' 'step up' ' transformer, the pri- 
mary coil being supplied with 1000 volts current and the 
secondary coil supplying a higher voltage, 5000 volts. 
This is accomplished by winding a proportionately larger 
number of turns on the secondary coil than is wound on 
the primary, the proportion being 1:5. 



ALTERNATING CURRENT. 



67 



It must be understood that the secondary coil has no 
metallic connection with the primary coil, and that what- 
ever current is generated in it, must be due to the induc- 
tive effect of the current in the primary circuit. To get 
the maximum effect of the current in the primary cir- 
cuit on the secondary winding is the first requisite in a 
good transformer. 

The coils are therefore both placed on an iron core in 
such a position that as many as possible of the magnetic 




too© VOtTS. 




TRA/^sroi<ntJ\ 



\000 TO ^0 VOLTS. 

RATIO Of TtRM* 
a.0'1 



TRAJlSFORnE^ 

1400 TO 100 <0CT4. 



I^IGURK 26.~PI,AN OF^ AI^TERN AXING CURRENT 
DISTRIBUTION. 



lines from the primary coil will embrace the secondary 
winding. The coils are usually placed close to each 
other and in fact, would be interlaced with one another, 
were it not for the fact that aside from difficulty of man- 
ufacture, the danger of contact between the high voltage 
current carried on the primary circuit and the lamp cir- 
cuits from the secondary windings would prohibit it. In 
practice we will find that the primary coil is extremely 



68 



AI.TERNATING CURRENT. 



well insulated from its neighboring secondary coil, so as 
to make it quite unlikely for contact between them. 

The theory of the transformer is quite complex when 
all of its internal actions are taken into consideration 
and many books have been written, filled with algebraic 
formulas in regard to the transformer and its actions. 

We may take up a few simple actions however, without 
the aid of mathematics. We have already spoken of self- 




$9 VOLT*. 



RATIO 20:1 



,IO00 Vbi-X4 




RATIO 10:1 

FIGURE 27. — FORMS OF TRANSFORMERS. 



induction of a coil of wire surrounding an iron core, and 
have shown that it takes an appreciable time for current 
to reach its maximum in a coil having self-induction. 
Also the apparent resistance oflfered to the breaking of 
the circuit. If an alternating current be supplied to a 
coil surrounding an iron core, we will find that owing to 
the self-induction of the coil, it will be impossible to pass 



AI^TERNATING CURRENT. 69 

as much current through it with a given voltage as would 
be possible with direct current of the same voltage. In 
fact, in a coil having for instance, 10 ohms resistance, 
we might be able to put but ^^ ampere through it with a 
voltage of 1000, provided the coil was wound on an iron 
core after the manner of a primary coil of a transformer. 
1000 volts of direct current would put 100 amperes 
through the same coil. This difference is due to the self- 
induction or * impedance" of the coil when supplied 
with an alternating current. The reason is, that with 
the current alternating 15,000 or 16,000 times per minute 
that the electro-motive force or voltage, although high, 
does not have time to force the current to its maximum, 
before having fallen to zero and exerted an electro- 
motive force tending to reverse the current in the coil. 
The amount of energy expended will be in this case, 
only a small amount and in a transformer will be termed 
the leakage or magnetizing current. 

The leakage will depend on several factors. In the 
first place there must be enough iron in the trans- 
former core to form a path of low magnetic resistance 
for all the lines of magnetism given out by the primary 
coil, so that with the secondary coil placed on this core, 
practically all of the magnetism of the primary current 
will effect the secondary winding. Great care must be 
taken in selecting the quality of iron, for the magnetism 
of the iron transformer core is being reversed each alter- 
nation of the current and some kinds of iron will mag- 
netize more quickly than others. It takes power to 
reverse the magnetism in the iron and this loss is called 
hysteresis loss, hysteresis being the loss occasioned by 
altering or reversing the magnetism of iron. This hys- 



7b AI^TERNATING CURRENT. 

teresis loss is smallest when a soft iron core is used and 
to provide against eddy currents in the core, it is lamin- 
ated in the direction parallel to the lines of magnetism 
in the core. The eddy currents in a solid iron core 
would be caused by the magnetic effect from the primary 
and secondary coils generating currents of electricity in 
the iron itself, which although of extremely low voltage, 
would have sufficient current strength to heat the iron 
and core, thus not only endanger the insulation of the 
transformer but also counteract part of the magnetic effect 
in the iron. Thus the cores of transformers and in fact, 
all coils w^hich carry alternating currents should be di- 
vided in small sections either by building them up out of 
thin sheet iron or out of soft iron wire. These divisions 
should not be made so as to break the continuity of the 
magnetic ciicuit, but must be made parallel to the lines 
of magnetism in the iron core. 

The leakage in the primary coil is of course partly de- 
pendent on its resistance, but this resistance has practic- 
ally no effect at all in the case, we have mentioned of 
a single coil wound on an iron core for the impedance 
due to self-induction in the coil, exerts by far the most 
powerful tendency to keep the current from passing 
through the coil. 

If now, on the laminated core of iron, we place a sec- 
ond coil and for instance, have the ratio of turns of wire 
in the high pressure as compared to the low pressure or 
second coil, lo to i, we will find that when the primary 
coil is connected to a looo volt constant potential alter- 
nating current circuit, that the low pressure coil forming 
the secondary winding will have a voltage of loo volts at 
its terminals and if we have a correctly designed trans- 



AI.TERNATING CURRENT. 7^ 

former of say, 5000 watts capacity (100—16 c. p. .amps) 
will find that with practically no current in the second- 
ary circuit, that there will be a leakage on the primary 
of about i^Q ampere at 1000 volts pressure. If now, 10 
lamps each taking >^ ampere at 100 volts are connected 
to the secondary winding, we will find that the current 
in the secondary circuit will now be 5 amperes and that 
the primary current has increased from j^o ampere to 
f%. If 10 more lamps are now connected to the second- 
ary, the primary current will be found to be ii^g ampere. 
In fact, as the current in the secondary winding is in- 
creased, the primary current is also increased and this 
increase in the primary should be as many watts as is 
added to the secondary load. The self-induction and 
impedance of the primary circuit is being decreased by 
the mutual inductiofi taking place between the second- 
ary and primary windings, for as the load increases in 
the secondary winding, just so much is the counteracting 
effect of the secondary winding on the primary. Thus 
owing to the decreased impedance of the primary coil, 
owing to the effect of the current in the secondary wind- 
ing more and more current flows through the primary 
coil, until at full load the primary winding is carrying 
its maximum current and the secondary is exerting its 
full contracting effect on the impedance of the primary 
winding. The efficiency of such a transformer should 
be about 97% at full load. That is, the secondary wind- 
ing should be delivering 97% of the energy --applied to 
the primary coil. 

Thus it will be seen that alternating current can be 
distributed at high pressures and then reduced at trans- 
formers to a voltage suitable for operating incandescent 



72 AI.TKRNATING CURRENT. 

lamps with but a small loss in transformation. The loss 
in watts in transmitting a certain amount of electricity 
through a wire of given resistance may be stated as vary- 
ing with the square of the pressure or voltage at which 
it is transmitted. 

Thus to deliver 5000 watts, i mile from the dynamo at 
1000 volts pressure, will take jj^ as much copper as that 
necessary to send the same 5000 watts at 100 volts pres- 
sure with the same loss. For several reasons, 1000 or at 
most, 2000 volts pressure is as high as is safe to go in 
generating current for ordinary lighting plants and most 
alternating current dynamos are made for either one or 
the other voltage. 

In most large alternating current stations the highest volt- 
age generated is about 6,600 volts which if either stepped up 
to any voltage from 6,600 to 150,000 volts or stepped down. 
In many cases it is consumed as it is generated. 

A transformer may have more than one secondary coil 
or a single coil may be divided into two or more sections 
and by varying these connections, it will be possible to 
get for instance, from the usual form of transformer used 
in America for incandescent lighting. 50 or 100 volts as 
desired by connecting the two sections of the secondary 
in multiple or series with each other. Fuses are usually 
placed on the primary wires only, in the modern type of 
transformer. In case of a short circuit in the secondary 
winding or the wires leading from it, the primary fuse 
would immediately be melted, and thus open the circuit. 
When the secondary wires enter buildings the usual 
method of fusing all circuits must be carried out, not as 
a protection to the transformer, but as a protection to the 
smaller tap wires leading to lamps, etc., which unless 



ai,te;rnating current. 73 

provided with fuse wires might in case of a short circuit, 
melt before the primary transformer fuse would open the 
circuit. 

The wiring from the transformers to the lamp should 
be carefully calculated, owing to the fact that the trans- 
formers on a constant potential primary circuit cannot 
provide extra pressure as the load increases so as to com- 
pensate for loss in the wiring. The wiring on all second- 
ary circuits should be done so as to provide for a very 
small drop, for in fact, the secondary voltage gradually 
falls as the load increases and although in the well de- 
signed transformers, this drop amounts to but from i % 
to 2 % , it is oftentimes sufficient, when combined with loss 
in the secondary circuit, to cause a marked diminuation 
in candle power of the lamps. 

Special transformers are often wound so as to give 
from 30 to 35 volts on the secondary winding, which is 
the voltage needed to operate the usual type of alternat- 
ing current arc lamps now on the market. 

Step up transformers are usually used in places where 
it is desired to send electricity for lighting, etc., a con- 
siderable distance from the dynamo. The voltage of the 
alternating current dynamo or "alternator'* is usually 
1000 or 2000 and this is raised in the step up transformers 
to pressure sometimes as high as 150,000 volts. The current 
at this pressure is then transmitted in some cases twenty or 
even one hundred miles and then the pressure is again reduced 
to that desired for lighting, etc. 

The usual alternating current dynamo as used for light- 
ing, supplies a single phase current as distinguished from 
alternating current dynamos supplying multiphase currents, 
which may have two^ three or more phases. 



74 



AI.TERNATING CURRENT. 




5rrfGLfr PHAS&. 
AtTERnATlMO 



Figure 28— Pi.an A. 




Uo)X.*\ 



COfLS 90 



Two PHAS6 
AtTtllWATlfSfr 
CtRRtnt 



Figure 28.— Pi,an B. 




3 PH/^SE. ^tjERM/Win^ Ct^V^JW^v^ 

Figure 28.— Pi,an C 



AI.TKRNATING CURRENT. 75 

A dynamo which supplies an alternating current which 
consists of a succession of single alternating impulses 
will be called a single phase dynamo and such a current 
is a single phase current. 

If, however, there are two windings or their equivalent 
on the armature, each of which is sending out a single 
phase alternating current, the dynamo is now a two-phase 
d3mamo and by designing the armature coils so that the 
rise of current in one armature winding is not coincident 
with the rise in the other winding, peculiar magnetic 
effects may be produced in a suitable form of magnet by 
providing it with two windings, which are supplied with 
current from the two armature windings of the two phase 
dynamos. Likewise, three windings may be placed on 
a single armature and thus make a three-phase dynamo 
generating a three-phase current. The figures 28 show 
the current wave of a single phase alternating current 
dynamo (plan a). Plan b, shows a two-phase current, in 
which the relative amounts of current during a revolu- 
tion are shown in the two windings. The waves of cur- 
rent in this case are in quadranture, that is, one coil's 
current wave is 90° ahead of the current in the other coil. 
Plan c, shows the relations of the currents in the coils of 
a three-phase generator. The currents are in this case 
120° ahead of each other. 



76 TYPES OF DYNAMOS. 



CHAPTER VI. 



TYPKS OF DIRECT AND AI.TERNATING CURRENT 
DYNAMOS. 



Direct current dynamos are manufactured principally 
in three types, shunt, series and compound wound. 

The shunt dynamo is found largely in isolated and 
central station electric lighting plants, operated on the 
two and three wire systems, and supplying incandescent 
lamps, small electric motors and constant potential arc 
lamps. 

These three types of machines are made in bipolar 
(two poles) and multipolar (more than two poles) design 
as respects field magnets. 

In the previous chapters, the reader has learned that a 
current is generated in the armature by the movement of 
coils of wire in a magnetic field which is usually pro- 
duced by electric currents flowing through coils encir- 
cling bodies of iron, called field magnets, and that the 
electric currents generated in the armature are taken 
from it by means of the commutator and brushes bearing 
on it. 

Consider a U shaped piece of iron forming the field 
magnet, wound with wire so as to form an electro-mag- 
net when supplied with the electric current. Now in 
the shunt dynamo, the two terminal wires of a magnet 
similar to this are attached to the armature terminals 



TYPES OF DYNAMOS. 77 

and form a shunt around the armature from whence the 
name * 'shunt dynamo" is derived. 

By previous application of an electric current to the 
coils surrounding the iron cores, they have been magnet- 
ized and iron once magnetized always retains a little of 
its magnetism, called "residual magnetism". If then, 
there is the feeble magnetism remaining in the magnet, 
it follows there must always be a slight magnetic field 
between the poles of the field magnets and as there is an 
armature revolving in that field, a current is generated 
which passes out to the commutator and by brushes is 
led oflf to the circuit. One path which this current can 
take is that through these field coils which at once causes 
them to be more powerfully magnetized and a greater 
magnetic field is thus produced, hence a greater amount 
of current is generated in the armature. By this step by 
step process, the machine slowly "builds up" to the 
proper potential until the normal magnetization is 
reached. 

A rheostat or a variable regulating resistance is in series 
with and connected in the field circuit which regulates 
the potential or voltage by varying the current through 
the fields. When a dynamo is running with no load, 
all the resistance in the rheostat is generally in circuit. 
Now as the load increases, whether it be that electric 
lights are switched on or motors are run, either of these 
will require dynamo current and the potential of the ar- 
mature falls slightly. To get more current in the fields 
so as to raise the potential, we must increase the current 
through them by manipulating the rheostat. A shunt or 
compound wound dynamo generally speaking, has its 
pressure remain constant and the current quantity varies 



78 TYPES OF DYNAMOS. 

as more or less lamps are turned on. The shunt or com- 
pound wound dynamo for supplying constant potential 
current usually depends on the varying strength of the 
field magnets for regulation, but the series wound dyna- 
mo supplying a constant current is often regulated by 
* 'armature reaction" alone, the armature reaction being 
the internal electrical action of the armature windings, 
which may be used for regulating. 

The series dynamo is used almost exclusively for series 
arc lamps, but series motors can be placed on the series 
dynamo, and operated. The field magnets are in series 
with the armature and full current of armature must pass 
through them. Again we find that the series dynamo 
usually generates a variable pressure and constant cur- 
rent. Arc lamps are run in series with the dynamo, and 
if this current supplying them fluctuated, as does that on 
a shunt machine it would produce great variations in the 
candle power of the lamps which would make a very un- 
satisfactory light. The arc lamp when burning on a ten 
ampere circuit has a resistance between the carbons of 
4^ to 5 ohms and to force the requisite lo amperes of 
current through the arc, a pressure from 45 to 50 volts 
(CXR=B) is required. If 10 lamps are to be run, the 
dynamo must supply the 10 amperes at a pressure of 500 
volts and the dynamo for this purpose usually has its 
brushes shifted so as to cut in additional active coils in 
the armature, which means an increase in pressure or 
voltage on the line for the extra lamps cut in the circuit. 
No rheostat is necessary in this case, as the regulation of 
the armature by the shifting of the brushes keeps the 
current constant through the fields, the magnetic field of 
the dynamo always containing the same number of mag- 



TYPES OF DYNAMOS. 79 

netic lines. In the series wound machine the brushes 
are shifted against the direction of rotation for an 
increase of load. 

The compound wound dynamo supplying constant 
potential current, though embodying the shunt and the 
series principles, is more a shunt machine than series. 
Its regulation depends upon its fields. Its voltage is con- 
stant and ampereage variable. In a well designed dyna- 
mo after the voltage is regulated by means of the rheo- 
stat, the machine takes care of itself. The armature 
rotates in a powerful magnetic field. In either the shunt 
or compound wound dynamo, it is possible to so propor- 
tion the field magnets and armature that the * 'non-spark- 
ing' ' point on the commutator is not shifting as the load 
varies, although in many makes of dynamos, as the load 
increases the brushes must be shifted forward in the di- 
rection of rotation, or sparking will result. This is caused 
by the magnetic effect of the armature distorting the 
flow of magnetic lines given out by the field magnets so 
as to alter the position of the neutral line in the arma- 
ture. In compound wound dynamos all the current gen- 
erated in the armature passes through the series windings 
on the fieldmagnets. The machines are so built that the 
series winding does the regulating and the magnetic field 
does not reach its full vStrength until the dynamo is deliver- 
ing its full current. The dynamo * 'builds up' ' by virtue of 
its shunt winding and as current is required from the dy- 
namo for the outside circuits, this same current passes 
around the series coil of the field magnets, increasing the 
magnetic field and consequently maintaining the pres- 
sure uniform. Compound wound dynamos may be com- 
pounded for any percentage increase in pressure from no 



8o TYPES O^ DVNAMOS. 

load to full load, thus compensating for the **drop" in 
voltage that occurs on the line when large currents are 
being passed through them. 

Alternating current dynanios consist principally of 
three classes, self excited, separately excited and com- 
posite or compound. They are almost invariably high 
voltage machines, from looo volts up and consist in an 
armature of as many coils in series as there are field 
magnets and these are much in excess of those on direct 
current dynamos. A great number of alterations of the 
current are required for practical work and consequently 
to keep the armature speed down to a reasonable point, 
a gieater number of magnet poles are used. Currents 
generated by the armature are led out in two wires to 
collector rings, where by brushes connected to the circuit 
the current is taken to the transformers, etc. The mag- 
netic field extends from one field magnet to its neighbor 
on either side of it. The field magnets which are usually 
wound in opposite directions on each successive pole, are 
excited in the self excited machine by taking the current 
of one or more of the armature coils and passing it through 
a current rectifier. It would be useless to excite the fields 
by the alternating current as the rapid reversals in the cur- 
rent unfit it for such service. The alternating current must 
be commuted to a direct current and the rectifier or two 
part commutator performs this function, by sending all 
the impulses through the field magnets in one direction 
and they are thus excited by a pulsating direct current. 
The residual magnetism in this case plays a part in the 
alternating dynamo as it does in the direct. As the ar- 
mature rotates in the magnetic field, weak alternating 
currents are generated passing through the rectifier, 



TYPES OI^ DYNAMOS. 8l 

thence around the field magnets, again developing great- 
er currents in the armature until normal magnetism is 
reached. The separately excited alternator is devoid of 
a rectifier and has its fields excited by an independent 
direct current dynamo. Regulation is obtained by vary- 
ing the current in the field magnets as the load varies by 
means of a rheostat in the circuit of the direct current 
dynamo. 

The composite field or compound alternating dynamo 
is analogous to the compound direct current dynamo, 
inasmuch as an additional winding passes around the 
field magnets in addition to the usual winding found on 
the separately excited alternating current dynamos. This 
winding is supplied with a pulsating direct current from 
a rectifier whicn commutes a portion of the output of 
armature current, the amount depending on the load in 
amperes. As the current is increased on the circuit, just 
so is the current increased in the fields and the potential 
is gradually increased to overcome the * 'feeder loss.'* A 
resistance is bridged or shunted across the rectifier which 
can be varied so as to produce different increases in the 
pressure at full load to allow for "drop" in line. 

Other classifications of alternators are made, namely: 
dynamos in which the field magnets are stationary and 
armature rotates, dynamos in which the armature is sta- 
tionary and field magnets rotate and those in which field 
magnets and armature are stationary and an irregularly 
shaped iron inductor rotates between the two. The 
principal of the * 'inductor' ' type of alternating current 
dynamo is that if the number of lines of magnetism is 
varied through the stationary armature coil that the 
same effect will be produced as when the armature coil 



82 TYPES OF DYNAMOS. 

moves so as to cut these lines of magnetism. The 
revolving iron "inductor" is so shaped that as it revolves 
it completes and then breaks the magnetic circuit through 
the armature coil and this of course must genei ate cur- 
rent in it. Alternating current dynamos are 1 milt for 
any phase and frequenc}^ but it is not timely to 1 ead the 
reader further than has been gone into in the pi eceding 
chapter, as other books cover this advanced woi k. 

It is frequently the , case that one dynamo is insuffic. 
ient to supply the circuits that it is feeding at certain 
hours during the run and it becomes necessary to place an 
additional dynamo on the circuit. In incandescent light- 
ing, the machines would be placed in multiple, but in 
arc lighting they would be connected in series. In the 
shunt wound dynamo an increase in load means an 
increase in amperes output with voltage constant, while 
in the series dynamo an increase in voltage results with 
the current constant. Therefore, if it is required to run 
an extra machine on a circuit, if it be a shunt or com- 
pound of the constant potential type, it is connected in 
multiple, but if the usual series dynamo, it is put in 
series. Instances where series dynamos are run in 
multiple or compound wound dynamos in series are few 
but explanation will be given their operation. 

SHUNT WOUND DYNAMOS IN MUI.TIPI.E. 

The directions to be followed in placing shunt dynamos 
in multiple is as follows: 

One dynamo already running — Start second dynamo 
up to full speed — Set brushes on commutator — Move rhe- 
ostat handle until voltage of dynamo is the same or 
slightly greater than that of dynamo already running. 



TYPES OF DYNAMOS. 83 

This can be indicated by a voltmeter. A pilot lamp is 
usually placed on shunt or compound dynamos and they 
will roughly indicate when dynamos can be placed in 
circuit. As soon as switch is thrown connecting both 
dynamos to the circuit, the load should be equalized on 
each by cutting in resistance in field circuit on the dyna- 
mo first running and cutting out resistance on dynamo 
just switched in. If the voltage of the second dynamo 
be less than that on the circuit, the dynamo will receive 
current from the first and operate as a motor turning in 
the direction of its previous rotation. In taking a ma- 
chine from the circuit proceed in reverse step. The 
Kdison three wire systems use shunt and compound 
dynamos. The two dynamos in this case, the positive 
dynamo supplying the -f- side and the negative dynamos 
supplying the — side, are started up as previously 
explained. 

Being independent of each other and working on separ- 
ate circuits, no especial precautions are necessary in 
starting dynamos. The potential should be kept alike 
on both machines and when possible, the current in 
amperes should be the same. If one dynamo carries 
raore current than another, that difference existi ig, is 
is carried by the + wire. If, as the load increases, addi- 
tional dynamos are to be placed in parallel on either side 
of the system they are placed in, the circuit in the same 
manner as has been described, one dynamo being in mul- 
tiple with the + dynamos and the other with the — 
dynamo. One dynamo may be made to supply a 3 wire 
system by using a switch that will connect -|- wire with 
= — wire making the neutral a common return for the two 
outside wires. This method is not to be recommended 



84 O^YPES OF DYNAMOS. 

unless the original wiring was designed with this object 
in view. 

Shunt dynamos may be connected in series when long 
distance transmission is to be accomplished. The field 
circuits should be connected so as to form one shunt 
across the dynamos so run in series and they will thus all 
be excited equally. All machines in this case should be 
of the same current capacity and each must be able to 
carry the maximum current on the circuit, or in the case 
dynamos of various sizes in series, the current must 
never rise above the carrying capacity of the smallest 
armature in curcuit. 

SERIES DYNAMOS IN SERIES. 

Dynamos to be thus connected must have same current 
capacities and the -j- terminal of one must be connected 
to the — terminal of the other. In a lighting plant, this 
is readily performed at the switchboard by plug con- 
nectors. This not so satisfactory as making other com- 
binations but is often done. If series dynamos are to be 
connected in multiple, let the armature of one dynamo 
excite the fields of the other and vice versa, so that if 
one generates not enough current, it weakens the field of 
the others and both are equalized. 

COMPOUND DYNAMOS IN MUI.TIPI,E. 

The compound dynamo embracing the characteristics 
of the shunt and series machine, the coupling together 
becomes an operation including both. In figure 29 two 
generators are connected for multiple working. One 
machine is running and the switches Ai for shunt circuit 
and Bi for series circuit are closed. The armature Di is 
then generating its normal electro-motive force and cur- 



TYPES OF DYNAMOS. 



85 



rents are llowing in the shunt field and the series field 
circuits. Armature D2 is then run at its normal speed, 
the switch A2 is thrown, allowing the shunt winding to 
excite the fields of dynamo D2. The switch C on the 
equalizer wire is closed and when switch B2 is closed, 
the machine takes its part ot the load. Before the sec- 




CONNECTIONS Olf TWO COMPOUND DYNAMOS 
IN MULTIPLE. 

end dynamo is coupled in circuit, that is, before switch 
B2 is closed, the voltage should be about the same as that 
of the dynamo D i first running. After the two are coupled 
in circuit, the load on each machine should be balanced 
by the rheostat. By examining the diagram of circuits, it 
will be seen that the equalizer wire practically places the 
two series windings in multiple, and this is necessary, 
owins^ to the fact, that in case two compound dynamos in 
multiple were feeding a circuit and were not provided 
with an equalizing wire, and one dynamo had its voltage 
slightly decreased from any cause, for instance a slipping 
belt, that the current in the series coil of the dynamo 



86 TYPES OK DYNAMOS. 

whose voltage was lowered, would necessarily be weak- 
ened and this of course would still further reduce the 
voltage of the dynamo in trouble. But in the case of 
the dynamos provided with an equalizing wire, the two 
coils being in multiple and of equal resistance, will have 
the total current output of the two dynamos divide 
equally between them and thus tend to keep the two dy- 
namos balanced. The equalizer should have a very low 
resistance compared, to the series windings so as to per- 
form its office satisfactory. In cutting out a machine the 
same steps are taken only in reverse order. Compound 
dynamos of different current capacities can be run in 
multiple, if the voltage is the same and the resistance of 
the series windings are inversely proportional to the cur- 
rent capacities of the several machines, in other words, if 
a dynamo produces half as much current as another, its 
windings should have twice the resistance of the other. 
The machines also govern each other, as when one ma- 
chine runs too fast, it does more work and consequently 
lowers its speed, and momentarily it robs the other 
machines of part of their load, which makes them run 
faster and thus producing equality. Compound dynamos 
may be connected with good results in the manner 
described under shunt dynamos in series. 

AWERNATORS IN MUIvTlPI^E. 
To couple direct current dynamos in multiple we said 
that their potentials should be alike, but in alternating 
current dynamos not only this is usually required, but 
the machines must correspond in phase and frequenc3\ 
To couple an alternating current dynamo in circuit 
with another, the impulses in both machines must rise 
and fall together or be "in step." The frequency, period 



TYPES OF DYNAMOS. 87 

and alternations are directly affected by the speed, for 
the faster the speed the ^eater the alternations, that is, 
frequency, and vice-versa. Now when one generator is 
coupled with another generator or motor and running in 
step with it, we say they are in synchronism. The instru- 
ment provided to indicate synchronism is called a 
synchronizer and is explained in chapter x. To discon- 
nect alternators when running in parallel, is not as diffi- 
cult as when coupling in. The main switch of dynamo 
is opened and then the switch on the exciter circuit to 
dynamo should be opened. It is a better plan while 
machines are running on single circuits to reverse this 
operation, throwing exciter switch first and then machine 
switch, as there are less chances of injury to alternator. 
The same efifects which cause alternators to work well in 
parallel causes them to be opposed and get out of step in 
series. 



88 TROUBI<H IN DYNAMOS. 



CHAPTER VIL 



CAUSES OF TROUBIvE IN DYNAMOS. — THEIR REMEDY 
AND PREVENTION. 



The rotating portion of any dynamo electric machine 
or motor is its vital part. In some machines, this ele- 
ment is the armature, in others the field magnets. In 
case the rotating part is the armature, it will be evident 
that means must be provided to take the current gener- 
ated from the moving conductors of the armature to the 
lamps, motors, etc., for which the dynamo is to supply 
current. This is done usually by means of brushes bear- 
ing on the commutator or collector rings, as explained 
in previous chapters. 

The first fault developed in a machine should be speed- 
ily removed, and the second fault never allowed to 
appear, as the machine will rapidly destroy itself. 

The following directions apply particularly to direct 
current dynamos of the * 'closed coil" type and do not 
apply to some * 'open coil" dynamos used for arc light- 
ing, etc. 

We have to-day, several different styles of brushes in 
general use. They come under two general heads, metal 
brushes and carbon brushes. 

Metal brushes are made usually of copper, either of 
several leaves of thin copper ribbon or a number of cop- 
per wires soldered together at one end, or a combination 
of wire and leaf copper. A patented brush of consider- 



TROUBI,^ IN DYNAMOS. 89 

able merit is made with leaves of copper arranged be- 
tween leaves of high resistance metal with a number of 
sheets of oiled or parafined paper interlaid for lubricating 
purposes. The idea of high resistance metal either side 
of the copper, is to stop the sparking by reducing the 
short circuiting action of the brush on coils that are in 
the weak field near the neutral point on the commutator. 

Carbon brushes are used to a great extent on street 
railway machinery, both on dynamos and motors. The 
brushes are cheap, self-lubricating to a great extent, and 
do not wear the commutators near as much as copper 
brushes. The sparking which results from rapidly fluc- 
tuating loads is not only lessened but is made practically 
harmless to the commutators, since the burning action of 
tho sparks seems to concentrate itself on the carbon and 
does not injure the commutator. For the best results, a 
good grade of carbon made especially for this purpose, 
should be used. The vapor of the carbon, generated at a 
spark, is undoubtedly of higher resistance than the vapor 
of copper and this must reduce the sparking to a great 
extent. The carbon brush has been applied to arc dyna- 
mos of recent construction with considerable success. 
On motors which are designed so as to be able to reverse 
their direction of rotation, such as street car motors, etc,, 
the carbon brush is a necessity and is usually set at right 
angle to the face of the commutator. 

Brushes should have more than sufficient cross section 
to enable full current of armature to be delivered through 
them continuously without undue heating, and the cross 
section of armature segments should be governed by the 
same rule. Every part of the whole width of the brushes 
should bear on commutator. When brushes are set od 



90 l*ROUBI.E IN DYNAMOS. 

commutators of direct current dynamos, they should 
usually be diametrically opposite each other and then 
placed evenly so that every part makes true contact. 
There should be no dirt on contact surfaces, for if there 
is, severe sparking and heating will result. Brushes 
should rest upon commutator with slight pressure, but 
not enough to cause undue cutting or heating. They 
should be removed at regular intervals for inspection and 
cleaning and if necessary, placed in a brush jig or form, 
and filed to a proper bevel, as brushes will, even with 
the best care, wear uneven, burr and collect dirt. To 
remove diit and grease from brushes, soak them in gaso- 
line or benzine. Sparking resulting from the causes 
above named is usually distinguished from the nature of 
the spark, which is present at the brush points during the 
full revolution of armature. 

A position known as the neutral point, exists on all 
commutators of direct current dynamos. This is the posi- 
tion of non-sparking in most cases, and generally varies 
with the load. If the brushes are ahead or behind this 
point, the sparking is considerable and can be remedied 
by shifting the brushes till the non-sparking point is 
reached. The following is the cause of this shifting of 
the non-sparking point. The field magnets tend to set 
up a magnetic field in one direction through the arma- 
ture and the armature owing to its conductors carrying 
currents of electricity, magnetize the iron armature core 
in such a manner as to oppose the magnetism of the field 
magnets and the resultant field, will depend on the rela- 
tive strength of the two opposing influences. Such an 
action called * 'distortion of the magnetic field" occurs in 
all direct current dynamos, and tends to shift the field of 



K'ROUBI.E IN DYNAMOS. 9 1 

force out of its natural position and it is evident that 
since it is caused by the current carried in the armature 
conductors, that it varies with the load, thus making a 
change in position of brushes necessary to keep them 
from sparking. If there existed no field distortion in 
dynamos, no movement of brushes v^ould be required. 

Though the care and inspection of the brushes has 
been spoken of, as much must be said of the commutator. 
No matter now nicely filed the brushes are, or how evenly 
they are set, or in what cleanliness kept, little will avail, 
if the commutator is uncared for. A well cared for com- 
mutator should have a glaze and polish, and with a good 
dynamo tender, this is always attainable. Sparking is 
sometimes caused by what is termed, a **high bar" or 
a flat bar on the commutator, and can, by close scrutiny 
usually be detected. At first you are warned by a spark 
appearing on the commutator, quite different from that 
caused by dirty brushes. By applying the fingers to 
commutator, once in every revolution a depression or an 
elevation will be felt. Commutators sometimes become 
**outoftrue" owing to improperly ^'smoothing down". 

This will be noticed by a rise and fall of the brushes 
when armature is revolved slowly. Again, if brushes are 
not properly trimmed or if not properly lubricated, the 
commutator will often present a bright coppery appear- 
ance and a disagreeable * 'sing' ' will be noticed, and when 
felt, it will be found rough, and plenty of copper dust 
will be found on brushes, etc. If in very bad condition 
commutator should be turned down in a lathe or better 
than this and without removing armature, a device simi- 
lar to a slide rest and usually furnished by makers of 
machines can be used with a narrow cutting tool. If 



92 TroubIvK in dynamos. 

only in rough condition with no deep groves, sand paper 
of different sizes from coarse down should be fastened on 
a suitable block for bearing pressure and applied until 
smooth. The use of a file, unless in experienced hands, 
is not recommended as it will often cause fine bits of cop- 
per or burrs to lodge in the insulation between the seg- 
ments and short circuit sections. ''Flats" are sometimes 
caused after arcing on a particular bar has occurred for 
some time, and if one .of the segments is of softer metal 
than the others, a flat will gradually develop. 

From time to time commutators should be calipered 
and the cross section of copper determined by subtracting 
the interior diameter of commutator from the exterior 
and multiply by the mean width of each bar. Excessive 
heating in commutator other than that produced by local 
causes, is many times observed and can be accounted for 
when it is found that commutator bars are not sufficient- 
ly large to carry the armature current without heating. 
Where a light load is constant on a machine, this may 
not be noticed until the commutator is worn through, 
but if on the other hand, a heavy load is always deman- 
ded, heating will take place, a new commutator should 
replace the old. 

The commutator should be supplied with a suitable 
lubricant and probably the best for the purpose, is vaso- 
lene, which is not only cheap but does the work well. 
A small quantity should be rubbed on a piece of cloth or 
canvas or even better, a piece of leather and on the 
slightest sign of cutting of brushes on commutator, it 
should be applied. Great care must be taken in keeping 
copper dust and dirt away from commutator and arma- 
ture, for if allowed to gather, it will surely make trouble. 



TROUBI^K IN DYNAMOS. 93 

In case of trouble with armature y first take a * 'mag- 
neto** described in previous chapter, which should be 
part of the equipment of every electric light plant, and 
find whether the windings of the armature are connected 
in any way to the core of the armature. This is easily 
done by connecting one terminal to the commutator 
segments and the other one to the shaft of the armature. 
If it is possible to get a ring, you may be sure that 
something is wrong in the insulation of either the 
commutator or armature, if the trouble has made itself 
known by a violent flashing at the brushes, and on ex- 
amination it is found that the fault is not in the brushes 
themselves and that one or more commutator segments 
are badly burnt, it may be inferred that the armature 
coils connected to the segments are out of order. In 
event of a short circuited armature coil, the particular coil 
will usually be found to be hotter than its neighbor or 
even burnt, or in case of an open circuit, the armature 
will refuse to generate at all. If there is simply a bad 
contact at the commutator or m the coil itself, there will 
be considerable local heating at the point of bad contact, 
which will u&ually be at the point the armature coil is 
joined to the commutator lugs. In case of an armature 
that has been heavily overloaded, it may be found thit 
the solder in the lug connections at the commutator, has 
melted and thus short circuited the coils, in this case 
clean out all the loose solder and removes all solder that 
make connections between commutator segments, so as 
to short circuit them. Ring armatures are much easier 
to locate trouble on than drum armatures, but it is hardly 
advisable for anyone but on experienced man to take 
any armature and try to repair burnt out coils. 



^ TROUBI^E IN DYNAMOS. 

In case it is found that a series arc light dynamo will 
not generate current after having been started up to 
speed, the first thing to determine is whether your cir- 
cuit to your lamps is "closed" or not. If it is "open", 
that is, if the circuit is not complete, the break should 
at once be located. In case a circuit seems to be partially 
open, which may be the case where several bad contacts 
or a defective lamp are in the circuit, it will often be 
possible to "ring" through it by means of a testing mag- 
neto, and from the fact that the ring of the magneto is 
much fainter than it should be, we know that the circuit 
contains much more resistance than usual. The usual 
testing magnetos as has been previously described, is a 
simple alternating current e^enerator of small size oper- 
ated by hand, which when generating current will ring a 
small bell. The winding of its armature is of fine wire 
and will generate sufficient current to ring the bell when 
connected to a circuit containing as high as 20,000 or 
30000 ohms resistance. Since the usual arc light circuit sel- 
dom has a resistance of over 500 ohms, and owing to the 
fact that a series wound dynamo will not "build up" on a 
circuit having any unusually high resistance, it follows 
that, although we may be able to ring through a circuit, it 
may be impossible to start the dynamo on it. In many 
cases of this kind current may be started through the cir- 
cuit by connecting the dynamo to the circuit and then 
short circuiting the dynamo by means of a piece of wire 
until it commences to generate current and then sudden- 
ly opening the short circuit where the momentary rise in 
pressure at the dynamo terminals due to its self-induction 
will start the dynamo current through the circuit. This 
plan should only be used as a last resort. Series dyna- 



TROUBI^E IN DYNAMOS. 95 

mos for arc lighting are usually provided with a switch 
which short circuits the series coils forming the field 
magnets and thus shuts down the dynamo by destroying 
the magnetism of the fields. This is the proper way to 
shut down a series arc dynamo, for if the circuit was 
broken while the dynamo was in operation, the rise in 
voltage due to the self induction of the dynamo and 
circuit is likely to injure the armature. For this same 
reason the field circuit of the usual shunt wound dynamo 
should never be broken while in operation, for the self 
induction ^'discharge" from the field magnet circuit is 
likely to injure the insulation of the machine. 

In stopping a shunt dynamo after a run, the brushes 
are often lifted from the commutators by careless dyna- 
mo tenders, while the field magnet windings are still 
receiving current from the armature before the armature 
has ceased revolving and the flash seen at the commuta- 
tor in such cases shows conclusively that the field coil 
insulator must be undergoing a much greater strain than 
when the dynamo is generating its maximum voltage. 

A separately excited alternating current arc light 
dynamo is usually provided with an arrangement which 
acts as a safety valve for the excessive extra voltage 
caused by an open circuit in the line.- It consists of two 
pointed carbons connected to opposite terminals of the 
dynamo. The points of the carbons, between which the 
maximum voltage of the dynamo will be found, are sep- 
arated a slight distance, the distance being such that 
when the dynamo generates an excessive pressure, the 
current will jump across the points and thus short-circuit 
the dynamo and save it from possible damage. 

The two well known types of open coil armature dyna- 



96 TROUBI.E; IN DYNAMOS. 

mos for arc lighting are the Brush and Thomson-Houston 
makes. The regulation of the Brush arc light dynamo 
is accurate and positive, and is performed in a simple 
manner. The field magnets which are of the series 
type and are provided with a shunt circuit of variable 
resistance between their terminals. In other words, the 
current in passing from the armature to the lamps has 
two paths to divide between. The amount of current in 
either path will depend on the relative resistance of the 
two circuits and the amount of current through the field 
circuits may thus be varied to suit the load which the 
dynamo is to have. 

The circuit in multiple with the field magnets has its 
resistance varied by means of the ''Dial regulator" which 
consists in its simplest form, of a magnet in the form of a 
selonoid through which the main circuit passes. The 
core of the selonoid is attached to a lever which varies 
the mechanical pressure on several piles of thin carbon 
plates, the usual form of dial regulator having four piles 
or columns of carbon plates in series, whose resistance will 
vary with the increase or decrease of pressure applied to 
them by the lever attached to the iron core of the selon- 
oid. These piles of carbon plates are thus capable of hav. 
ing their resistance varied and being in multiple with the 
series coils whose resistance is constant, we have a means 
of regulation. This style of regulator, when given proper 
attention, keeps the current practically constant at all 
loads, and should never be allowed to get out of repair. 
From time to time carbon plates may have to be added, 
and the contacts and moving parts of the regulator 
should be inspected often, to insure proper working 
when needed. 



TROUBLE IN DYNAMOS 97 

The arc light dynamos such as the Brush, Thomson-Houston, 
Excelsior, Wood, Edison, Standard, Ball and a few of smaller 
concerns have been very largely used in the United States but 
have since been replaced by modern direct and alternating 
current machinery. The age is tending toward alternating cur- 
rent machines because of their convenience and application to 
power and lights. But from a historical standpoint it is well to 
be acquainted with the various types of electrical machinery, 
their advantages and disadvantages. However, it must be said 
that there are small concerns throughout the country that 
are still operating some one type of the above mentioned 
machines. 

The armature consists of but three coils which, in the later 
type, are wound on a large iron ring, and are thus known as 
ring armatures, although electrically, they do not resemble the 
Gramme winding in the least. The three coils are placed 
equidistant from each other on the ring and each of the three 
main coils is divided into ten smaller coils in series, five of 
which are placed on either side of the ring diametrically oppo- 
site each other but connected in series. The three terminals of 
the three main coils on the pulley end of the armature, are all 
connected to a metal ring which serves as a common junction 
for the three main coils. The remaining three terminals at the 
commutator ends are connected to the three commutator seg- 
ments. The brushes, four in number, are in pairs, the leading 
brushes of each pair being called the secondary brushes and the 
trailing brushes are called the primary brushes. The brushes 
should be set with great care and also the nozzles to the air 
blast whose office is to direct a blast of air at the point of the 
brush just as the brush is passing from one segment of the 
commutator to another and thus reduce the sparking. The 
regulation is affected by moving the brushes slightly in direc- 
tion of rotation and also moving the primary and secondary 
brushes of each pair with relation to each other, which tends 
to allow the armature to generate more or less current. The 
usual Thomson- Houston dynamo will not run safely for any 
length of time on less than about % its maximum load unless 
provided with a "light load switch" which simply cuts out a 
portion of the field winding of the dynamo and thus weakens 
the magnetism. 



98 TROUBI,^ IN DYNAMOS. 

The spark at the commutator should vary from }i to X 
inches long, depending on the load. At full load the 
spark should be about j\ inches long. Great care should 
be observed in keeping all dust and dirt from the com- 
mutator supports and from all moving parts of the regu- 
lators. The automatic movement of the brushes in the 
Thomson-Houston dynamos is done by moves of a regu- 
lator magnet, which is in turn supplied with current 
intermittently by means of a wall controller located in 
any convenient position near the dynamo. 

The Excelsior Dynamo regulates by means of an auto- 
matic cutting in and out of convolutions or windings of 
the field magnets. 

The Wood dynamo and the Standard arc light dyna- 
mos both provide automatic regulation by means of 
shifting the brushes on the commutator of closed coil 
Gramme ring armature. 

The repairs of arc light dynamos are confined gener- 
ally to the armature and commutator and as a general 
rule, it will be found that such trouble as may occur, 
other than that due to over-loads, can be traced directly 
to carelessness on the part of the dynamo tender, in 
cleaning dirt and oil from his dynamo. Too much care 
cannot be bestowed in cleaning and keeping clean all 
dynamo electric machinery. 

A careful dynamo tender is a necessary adjunct to any 
well regulated electric light plant, and a greater mistake 
cannot be made than to place inexperienced men in 
charge of high voltage machines. 

An arc light dynamo may * 'flash" if carrying too 
heavy a load or if oil or dirt is present on the commuta- 
tor and brushes. 



TROUBI,^ IN DYNAMOS. 99 

Arc light dynamos of all types which generate pres- 
sures of 500 volts and over, should be handled with care, 
and it is always advisable to use rubber mats to stand on, 
when adjusting brushes, etc., while the dynamos are 
running. It is also a good plan to make it a rule never 
to use both hands if it can be avoided, in handling arc 
lamps, dynamos, transformers, etc., on live circuits. By 
placing one hand in the pocket and keeping it there 
when working on circuits of high pressure, there will be 
little chance of injury from touching two points at the 
same time in a circuit having a high difference of poten- 
tial. It must of course always be understood that it is 
extremely foolhardy to touch any part of a lamp or wire 
on a live circuit, unless standing on a thoroughly insu- 
lated floor, or in case of outside lamps on live circuit, a 
wooden box should always be used to stand on when 
adjusting them. Many fatal accidents have occurred 
through carelessness or neglect on the part of men not 
following these directions. 

Series wound dynamos may have their field magnets 
partially short circuited by over-heating and this will 
usually show itself by the machine refusing to generate 
its usual current. Rewinding the field magnets is the 
usual remedy. Portions of coils may be cut out by 
grounding on the core or frame of dynamo in two places. 
This can be located by means if a magneto or a simple 
battery and bell. 

If a shunt wound machine when running separately 
from other machines, refuses to "build up'* open the main 
switch leading from dynamo, and usually the trouble 
will be righted, which in this case was probably caused 
by a short circuit of some nature on the external circuit. 



100 TROUBI,^ IN DYNAMOS. 

If the machine refuses to generate after opening switch, 
look for trouble in socket of the pilot lamp. The reader 
will understand that when a large motor is not revolving, 
the resistance is low, and if a shunt dynamo should be 
started up with this motor connected, it would likely re- 
fuse to generate, consequently many motors now made 
are provided with a magnetic retaining switch which 
automatically disconnects motor from circuit when cur- 
rent for some reason, is thrown off. Again there may be 
an open circuit in the 'field magnets, or the magnetism 
(residual) may have become reversed by the close prox- 
imity of another machine. It will be noticed, if tried, 
that under these conditions, there will be little magnet- 
ism exhibited, even less than w^hen machine is not run- 
ning, being due to the neutralizing effect of the residual 
and current magnetism. 

Seek first to understand the principals upon which 
your machine depends, as it is then more possible to rem- 
edy the troubles that your machine is subject to. Field 
magnets, armature, commutator and current collecting 
devices make the dynamo. Understanding each of these 
you understand the whole. If the reader will grasp the 
facts in the preceding chapter, he can much easier cope 
with the troubles that will likely come. 



TYPES OF ARC LAMPS 



lOI 



CHAPTER VIII. 



ARC LAMPS FOR DIRECT AND ALTERNATING CURRENT. 
INCANDESCENT LAMPS. 



One of the most common uses of the electric current, 
is for illumination by means of the arc lamp ; and a rather 
detailed account of what should be expected of an arc 

lamp, will be of interest to every 
man in charge of dynamos used for 
either arc or incandescent lighting. 

By far the greater number of arc 
lamps in use today are supplied from 
constant current dynamos. That is, 
a dynamo generating practically a 
constant number of amperes, and a 
voltage that varies with the number 
of lamps in the circuit. These dyna- 
mos may be of either the direct or 
alternating current type. A 125 arc 
lamp dynamo was exhibited some years ago the voltage of which 
would be about 6,250 volts when running the 125 lamps. The 
current was 9.6 amperes. Assuming that the reader is fam- 




ARC LIGHT. 



102 TYPES OF ARC I.AMPS. 

iliar from study of previous chapters of the difference 
between constant current and constant potential dyna- 
mos, it will be evident that an arc lamp operating on a 
constant current dynamo, must have a mechanism capa- 
ble of performing several different functions. The * 'Vol- 
taic arc", which is so called from the noted philosopher, 
Volta, is formed in the usual arc lamp by separating the 
points of two carbons from j^g to ^q inches, through which 




FIGURE 30.— VOWAIC ARC. 

current is passing and when supplied from a suitable source 
of electricity, the current instead of being broken, jumps 
the space between the carbon points and generates in- 
tense heat, which makes them emit the usual dazzling 
light, known as the arc light. 

Figure 30 shows the appearance of the arc as viewed 
through a pair of dark glasses. The light is not given 



TYPES OF ARC I.AMPS. I03 

out directly from the current as it passes from one car- 
bon point to the other but is given ofif by the intensely 
heated carbon points. The cut shown is the appearance 
of an arc when supplied from a direct current dynamo 
and when supplied with alternating current, the form 
of the points and the diffusion of the light is quite dif- 
ferent. 

In case of lamps being supplied with direct current, 
the positive carbon burns practically twice as fast as the 
negative carbon and gives out a great proportion of the 
light. The positive carbon being the hottest and giving 
the most light, it will always be found to be the best 
plan to have the upper carbon positive and thus get the 
benefit of most of the light by having it thrown down. 

In the alternating current arc lamp however, the light 
thrown off by the upper carbon is the same as from the 
lower. This will be evident when we consider that the 
carbons are changing their polority with each alternation 
of the current, and that for this reason both carbons will 
be at the same temperature and give out practically the 
same amount of light. It will thus be seen that unless 
provided with a reflector over the arc, that as much light 
will be thrown up in the air as will be thrown down from 
the lamp where it can be used.. 

The candle power of the arc will depend on the energy 
expended in the current passing from one carbon to the 
other. This is easily represented in watts, which will be 
the product of the number of amperes and volts. The 
voltage at which most makes of carbons give the best 
results is from 40 to 50 volts and most arc lamps for work 
on direct current dynamos are designed to keep the car- 
bons far enough apart to maintain at least 45 volts be- 



I04 TYPES OF ARC LAMPS. 

tween the carbon points, when proper current is passing. 
Assuming that a lamp has a difiference of potential at its 
carbon points, of 45 or 50 volts, a constant current of 6.8 
amperes passing from one carbon to the other will pro- 
duce what is known as a 1200 candle power arc lamp or 
a lamp taking 9^ or 10 amperes at 45 to 50 volts, is 
known as a 2000 candle power lamp, and the large 
majority of arc lamps in use will be found to be 10 am- 
pere lamps rated at 2000 candle power. The 1200 candle 
power lamps spoken of, may also be known as an arc 
lamp taking from 300 to 340 watts, depending on the 
variation in voltage between 45 and 50 volts. The 2000 
candle power lamp takes usually about 450 watts, and it 
should be borne in mind that the watts used in any arc 
lamp is the true key to its candle power. 

With a good grade of American made carbon, the arc 
at 45 volts should be about f^ inches long and burn per- 
fectly quiet without the slightest '"blazing," ''flaming" 
or ''hissing." With the usual grade of carbon men- 
tioned, a lessening of the distance between the points of 
the carbon so as. to reduce voltage below 43 or 44 volts, 
will cause a peculiar ' 'hiss' ' to be heard. This hiss stops 
as soon as the carbons are separated again to such a 
length as to raise the voltage to 45 volts. 

If the length of the arc is increased to any extent, an- 
other effect known as blazing will be noticed. The volt- 
age usually rises to 50 or over before a good grade of car- 
bon will blaze or flame. It is thus seen that the voltage 
of an arc lamp on direct current should be kept between 
the hissing point and the blazing point of the carbon, to 
give a steady and satisfactory light and inasmuch as the 
carbon is always being consumed when the lamp is burn- 



TYPES OF ARC I^AMPS. I05 

ing, suitable means must be provided, firsts to separ- 
ate the carbon points when the current is turned on, 
secondy to keep the carbon points a proper distance apart 
to maintain a steady light and thirdly^ to cut the lamp 
out of circuit when the carbons have been consumed or 
or when any accident has occurred to disable the lamp. 
These three functions of the lamps mechanism have been 
developed in many different ways, a few of which will be 
mentioned as illustrating the practice of to-day in arc 
lamp construction. 

The general principle of all arc lamp feeding mechan- 
ism may be more readily understood by looking into 
what is taking place. Assuming that we have a pair of 
plain carbon rods, figure 30, one above the other between 
whose ends the arc has been established. As the carbons 
burn away, the length of the arc increases and so does 
the resistance. If the current in amperes remains con- 
stant and the resistance is increasing, it is evident that 
the voltage must be increasing with the resistance. Now 
if we have connecting the carbon points, a shunt circuit 
of very high resistance as compared with the arc, and 
this shunt resistance is made up of a very large number 
of turns of fine wire around an iron core, it is evident 
that the more resistance the arc itself contains, the more 
the current through the shunt will be, for we know that 
the current divides according to the relative resistance 
of the two paths shown. Thus, as the voltage increases, 
the magnetism must also increase and we here have a 
means for operating feeding mechanism for regulating 
the strength of arc and maintaining a practically uni" 
form voltage at the carbon points. 

The perfecting of the feeding mechanism of arc lamps 



I06 TYPES OK ARC LAMPS. 

has been the work of some of the brightest intellects the 
country affords, and to-day we will find that there are 
several general types of lamp feeding mechanism used, 
most types being fed by the actions of one or more mag- 
nets on a releasing mechanism and all types having an 
upper carbon rod to which the carbon that is fed, is 
attached. We will describe a few lamps used for series 
arc lighting. 

The first type and the one most generally used, is 
known as a "Clutch" lamp. A retaining device, termed 
the "clutch" grips the upper rod and raises it the proper 
distance to separate the carbon points, and form the nor- 
mal length of arc of probably 45 volts. As the carbon 
burns away, the length of the arc increases and the volt- 
age gradually rises until the shunt circuit magnet is so 
strengthened as to slightly loosen the grip of the clutch, 
and the rod, owing to its weight, slips down and thus 
reduces the length of the arc, which weakens the shunt 
magnet and thus causes the clutch to grip the rod again 
and hold the upper carbon rod stationary. In this type 
of lamp, a "series coil" will nearly always be found 
which carries the main current that flows from one car- 
bon to the other and which is always magnetized when 
the lamp is in operation. This coil separates the carbons 
on starting the lamp and usually has no other office. 

In differential arc lamps, the series coil is wound on the same 
spool with the shunt and the windings are so connected 
that the series winding opposes the shunt, and the result- 
ant magnetism will be the strength of the shunt 
minus that of the series, the shunt winding current of 
course increasing with the length of the arc. In this 
lamp the series coil separates the carbons to the point 



TYPES OF ARC lyAMPS. 



107 



where the shunt winding strengthens to such an extent 
as to make any further separation impossible. The 
increase in the shunt as the arc lengthens tripping the 



I 



-o 



[l 



CARftOM 



\. 







WASHER 
Cuirttj 




o 6; 




<^ 



/RON 



tA(?60r(b 



C'RCui- 






3HUN- 
COM— 



FIGURE 31. — CONNECTIONS OF CIRCUITS OF DIFFEREN- 
TIAI. ARC LAMPS. — CI.UTCH TYPE. 



clutch. Such an arc lamp is called a Diflferentially 
wound arc lamp. The same effect may be obtained by 
winding the shunt on one spool and the series on another 



io8 TYPES Olf ARC LAMPS. 

with the magnetic action opposing each other. Tht: 
well known American clutch lamps, operated in this way 
with differential magnets are the Brush, Wood and West- 
ern Electric. 

Two well known clutch lamps, the Thomson-Houston 
and the Standard arc lamps depend on simple shunt 
magnets to release the clutches. 

In the Thomson-Houston, or the **T. H." lamp as it is 
often called, a separate series winding is put on the out- 
side of the shunt winding and is used solely to separate 
the carbons, after which it is cut out of circuit until the 
carbons are to be separated again. This is not what would 
be called a differential lamp. The Standard arc lamp 
has a separate series coil which is always in circuit when 
the lamp is burning and simply separates the carbons, 
and the shunt spools do the releasing of the clutch. 

The Geared lamp, another well known type of arc 
lamp has a train of gearing and an escapement connected 
to the upper rod. The weight of the rod being enough 
to operate the gear, the magnets being used to separate 
the carbons and stop and start the gear according to the 
length of the arc. The Wood Geared lamp, the Excelsior 
and some other makes of lamps not as well known, are 
of the geared type. 

In general, it will be found that geared lamps are more 
liable to trouble than clutch lamps when placed in ex- 
posed positions, owing to the fact that the escapements 
and racks cut on the rods usually found in this type of 
lamp, often becomes clogged with dirt. When placed in 
protected positions however, they may give good satis- 
faction and furnish a steady light. Nearly all lamps 
now on the market for use on constant potential circuit*' 
are of the geared type. 



TYPES O^ ARC LAMPS. IO9 

When lamps are to be run on constant potential cir- 
cuits, they are usually furnished with a special grade of 
carbon and when placed on no volt circuits, are connected 
generally two lamps in series with 1^4 or 2 ohms 
of resistance wire, and these pairs of lamps with resist- 
ance, then take from six to ten amperes at 1 10 volts. 
The office of the resistance is not only to cut down the 
voltage to about 90 and thus provide a proper voltage lor 
the two lamps to run on, (two lamps, each taking 45 
volts, using the 90 volts,) but also to provide a regulat- 
ing action which tends to make the lamps pass a uniform 
amount of current through them. The necessity for 
such action will be appreciated by placing an ammeter 
in circuit with a pair of lamps when operating on a con- 
stant potential circuit of 1 10 volts, as is usually used in 
incandescent lighting. Whenever a lamp feeds, it will be 
found that the current at once rises in the lamp circuit, 
for when a lamp feeds its carbons together, the resistance 
of the arc is lessened and there being a constant voltage 
at the mains, the current at once increases. By placing a 
constant resistance in series with the lamps, the effect of 
one of the lamps feeding, does not have as much influ- 
ence in increasing the current as would have been the 
case, provided the two lamps were operating on a con- 
stant potential circuit of 90 volts. The usual type of 
constant potential arc lamp when designed for operating 
two in series on 1 10 volt circuits, has a differential feed- 
ing mechanism, but there are one or two types whiclf 
use a simple shunt magnet for not only forming the arc, 
but for feeding the carbons. 

In this case, the carbons are always separated when 
the lamp is not burning and the instant the current is 



no TYPES OF ARC LAMPS. 

turned on, the shunt magnets are energized and form the 
arc. As a general rule, constant potential arc lamps are 
not nearly as reliable as series arc lamps, for several 
reasons. The constant potential arc lamp has, as a gen- 
eral rule, been brought before the public by companies 
formed within the last few years for the especial purpose 
of manufacturing this class of arc lamp. Having had no 
previous experience in arc lamp construction, they 
have often turned out inferior made lamps, although in 
many cases to-day, they will compare favorably with the 
standard makes of series lamps, which are manufactured 
by companies long before the electrical public. 

The constant potential arc lamp thoroughly and suc- 
cessfully fills a place which the series lamp does not, but 
there is also an immense field for the series arc lamp 
that the direct current constant potential arc lamp cannot 
touch. 

In many towns, the amount of lighting is too small to 
pay dividends on both an arc light plant of the series 
type and an incandescent plant also, and it is certainly 
a commercial success to furnish both arc and incandes- 
cent lighting from a constant potential incandescent 
lighting dynamo, whether it be of the direct or alternat- 
ing current type. 

It is also a great advantage to be able to pay for your 
arc lighting on the meter basis, and until recently the 
only practical meters were those used to measure con- 
stant potential current. 

Another advantage of constant potential arc lamps, is 
that when it is desired to turn them off it may be 
done as easily as in the case of the incandescent lamp 
and of course on a meter basis, when your lamp is turned 
off, the expense stops. 



TYPES OF ARC IvAMPS. Ill 

The fact must be acknowledged that there is a loss of 
from 150 to 200 watts in the resistance in series with the 
pair of lamps when they are in operation, but the in- 
creased efficiency of the incandescent dynamos over the 
usual series arc machine helps to make up the difference. 

The constant potential arc lamp for alternating cur- 
rents has been greatly improved during the past year, 
and there are to-day several makes of alternating lamps 
that will give satisfaction under all usual conditions. 

One great objection to the alternating current arc lamp 
has been that the humming noise given out by both the 
arc itself, and the mas^nets used in the feeding mechan- 
ism was so great that the lamps were not' satisfactory for 
inside work. 

The use of a better grade of carbon and a mechanism 
with fewer moving parts, has in a measure overcome this 
objection. It was found that the shorter the arc, the less 
humming noise was given out by it and the practice 
to-day. is to use a carbon which will burn without hissing 
at about 28 volts, and use a special transformer which 
gives about 32 to 35 volts on the secondary and operate 
the lamps on this circuit. A small resistance is usually 
placed in series with the lamp. The lamps usually take 
from 10 to 15 amperes, depending on the candle power 
desired. 

The reason for a magnet in the alternating current 
lamp emitting a humming noise, may be briefly des- 
cribed. If a magnet coil carrying an alternating current, 
has for its core a bundle of loose iron wires, each alterna- 
tion of the current will tend to set the individual wires 
in vibration and it is this effect which often makes a 
magnet^ carrying alternating current, emit a humming 



112 



TYPKS OF ARC I.AMPS. 



noise. For this reason transformers will hum unless the 
core stampings are tightly bound together so as to pre- 
vent this vibration. 

If a coil which is to carry an alternating current is 
wound on a metal spool, it should be slit so as to prevent 




HEAT 



FIGURE 32. — DIAGRAM OF CIRCUITS OF HEAT 
MOVEMENT I.AMP. 

current from being generated in the spool, which might 
otherwise act as a secondary coil of a single turn. The 
feeding mechanism of alternating current arc lamp? 
should be as free from magnets as possible for any mag- 
net especially with an iron core will have sufficient self 
induction which, if it be a series coil, will act in a great- 



TYPES OF ARC I.AMPS. II3 

er or less degree so as to choke bi*ck the current in the 
circuit. Then again as the same series coil will not act 
the same on 16,000 alternations per minute as it will on 
15,000, the lamps will have to be adjusted dififerent for 
each variation in the number of alternations found in 
various plants. 

The heating effect of an alternating current of a given 
strength however, is the same as the same amount of 
direct current, and various methods of feeding arc lamps 
by means of heat generated either at the arc itself or by- 
passing the main or shunt current through a resistance 
have been experimented with. The heat generated by 
passing a current through a resistance will vary with the 
square of the current, or in proportion to the watts used. 
Thus if we pass two amperes through five ohms resistance, 
we will be expending 20 watts (C2R=(2X2)X5=20, if 
now, the current is increased to four amperes, we will find 
that although the current is doubled, that the watts ex- 
pended and thus the heating effect will be increased four 
times the watts, being 80. One arc lamp in which the 
plan of a heat feeding mechanism is thoroughly worked 
out, is the lamp manufactured on the Nutting *'heat 
movement'* patents whose feeding mechanism is purely a 
heat movement. The lamp is also probably the only 
practical lamp whose feeding mechanism feeds the car- 
bons continuously while burning, although the rate of 
feed may vary considerable. 

The plan of the lamp may be understood from figure 32 
which shows the plan of circuits. The lamp uses a shunt 
circuit for its feeding and separates the carbons in start- 
ing the arc by pulling down the lower carbon by means 
of a series arc drawing magnet in the bottom of the lamp. 



114 TYPES on ARC I.AMPS. 

The shunt circuit has a total resistance of about 120a 
ohms, a portion of which is wound around a heating pin, 
one end of which is embedded in the surface of a wax 
disc which is mounted on a shaft and geared to the upper 
rod. The pin being stationary, the wax disc is not 
allowed to turn until the heat of the current passing 
through the heating pin melts the wax around its end. 

The pin being in the shunt circuit, will carry more or 
less current as the arc is longer or shorter and as the 
heat in the pin varies with the square of the current 
passing through it, the field is very sensitive and con- 
stant. The end of the pin does not plow a furrow in the 
wax disc, for the melted wax surrounding the pin fills in 
behind it and thus a wax disc lasts an indefinite length 
of time. These lamps may be made for either direct or 
alternating currents of constant current or constant 
potential type. 

A very important and at the same time a very little 
thought of subject in connection with arc light, is that 
of carbons. A good carbon is an absolute necessity in 
obtaining good results in arc lamps, and a carbon which 
will give good results under one condition, may not in 
another. A soft carbon usually burns faster and gives a 
steadier and more perfect light than one that is hard. 

A * 'coppered' ' carbon burns much longer than the same 
size and make that does not have a copper coating. The 
higher the quantity of current to be carried in a carbon, 
the larger its diameter or the harder its texture should 
be. If the burning carbons are exposed to a wind, they 
will burn much faster than in a still atmosphere, and for 
this reason, if for no other, the globe should be added. 
For constant potential lamps either for direct or alter- 



TYPES Olf ARC I.AMPS. II5 

nating currents, a special carbon should be used. For 
direct current work, a cored carbon should be used for 
the upper or positive carbon and a solid carbon for the 
lower. A cored or treated carbon is usually a moderately 
hard grade of carbon having a core or hole extending 
through its length. The core of the carbon is a much 
softer made carbon than the main carbons. This hole in 
the positive carbon forms a permanent body and crater, 
and thus steadies the arc. The core being softer, makes 
an arc that is longer and less noisy than a hard solid 
carbon. In alternating current lamps, cored carbons 
should be used for both upper and lower carbons, to ob- 
tain the best results. At present, foreign carbons made 
in Germany and Austria, are being sold in large quantit- 
ies in America for constant potential lamps. Their ad- 
vantage over American makes, are longer life, better 
light, less dust and dirt and altogether a much better 
made carbon than the American makes. This is largely 
due to the fact that American carbon manufacturers have 
not experimented sufficiently as yet, to make as finished 
a product as the foreign makes. 

incande;scknt i,amps. 

The incandescent lamp is so called, from the fact that 
a filament usually made of carbon, is heated to incandes- 
cence by the passage of a current of electricity through it 
and thus gives out light. The perfection of the incan- 
descent lamp has taken an immense amount of experi- 
ment and money, and there seems to be even yet a 
chance for material improvement in this line. 

The first practical incandescent lamp was without 
doubt made by Thos. A. E)dison, and to him and his 



Il6 TYPES OI^ INCANDESCENT I,AMPS. 

associates belongs the most of the credit of bringing the 
incandescent lamp to its present perfection. The fila- 
ment of carbon is placed in a glass bulb from which all 
the air possible is exhausted, the wires connecting the 
ends of the carbons to the source of electricity being 
passed through the glass and making an air tight seal 
with it. The only metal found so far w^hich can be used 
to maintain a perfectly air tight joint, is platinum, which 
is a very expensive metal, its value being about that of 
gold. The reason that platinum must be used, is owing 
to the fact that it is the only metal which expands and 
contracts at about the same rate as glass. Inasmuch as 
the lamp is being heated and cooled as often as turned 
on and off, it follows that the *'inleading wires'* must be 
of this metal to prevent the glass cracking near the wires 
and letting air into the bulb. The usual lamp used in 
the United States, is the i6 candle power lamp, although 
incandescent lamps may be made of almost any candle 
power from J^ up to 500 or more. The modern incan- 
descent lamp of to-day takes from 2.9 to 4 watts of cur- 
rent per candle power given out and the life will vary 
from 300 hours in the 2.9 watt lamp to 1200 hours in the 
four watt lamp. 

In studying the most economical method of lighting 
by means of incandescent lamps, it will be found that 
the cost of the lamp itself is but a small portion of the 
cost of 500 or 600 hours lighting and in many cases a 
three watt lamp would be more economical than a four 
watt lamp to run, even if the three watt lamp cost $1.00 
each and the four watt lamp were furnished free. At 
two cents per ampere hour at no volts, a 16 candle power 
three watt lamp will use in 600 hours burning, about 



TYPES OF INCANDESCENT LAMPS 



117 



$5 20 worth of current. A 16 candle power lamp using four 
watts per candle power, will have used nearly $7.00 worth 
of current in the same time. The general public is gradu- 
ally waking up to this fact and demanding a high efficiency 
lamp rrther than one having a long life and low efficiency. 
It is evident that an electric light station, selling current 
by meter, can afford to give away four watt lamps to its 
customers rather than have them buy their 
own lamps of higher efficiency. Generos- 
ity (?) of this kind should be carefully 
investigated. 

Owing to the active legal proceedings of 
the owners of the Edison patents in America, 
most of the incandescent lamp manufacturers 
not leasing from the Edison Company, were 
enjoined from manufacturing lamps early in 
1893, and as a result great activity was 
shown by various inventors in devising new 
lamps which did not infringe the Edison 
patents. 

The Westinghouse Electric Company, the 
largest rival of the General Electric Com- 
pany, which owns the Edison patents, was 
one of the first to bring out a new lamp. 
It has been known as the Westinghoose * 'stopper*' lamp, and 
the principle may be readily seen from figure 33. The bulbs 
in this lamp are provided with a heavy moulded glass neck, 
in which is fitted a glass stopper which contains the two iron 
interleading wires. The inner part of the neck of the bulb 
is ground, so as to make a tight fit with a stopper, which is 
also ground. 




FIGURE 33. 
WESTINGHOUSE 
STOPPER LAMP. 



Il8 TYPES OF INCANDESCENT LAMPS 

The claim is made that a gas is used in the bulb instead of 
a vacuum being produced and that the air which may leak in 
after the stopper is sealed in by means of cement poured 
over its top is not enough to injure the successful operation 
of the lamp. This lamp was used for all of the incandescent 
lighting at the World's Fair at Chicago, in 1893. '^^^ Novak 
lamp is a gas lamp also, the claim being made that bromine 
gas is used in the bulb instead of the vacuum, Practical 
tests of this lamp are being made in many places and the 
results are likely to teach valuable lessons to the lamp manu- 
facturers. 

Incandescent lamps using metal filament have recently 
come into commercial use. Filaments of fine drawn wire of 
either tungsten or tantalum are suspended in a vacuum 
similar to the carbon filament lamp. The manufacturing of 
these lamps is the same as that of the carbon lamp with the 
exception of the suspension of the filament. The filaments 
are made much finer and longer than those made from carbon 
because the resistance of the metal is not as great. The light 
is much brighter with less power consumption than the carbon 
lamp — usually about two watts per candle power. Experi- 
ments have been made with nitrogen filled bulbs and metallic 
filaments which have shown a much higher efficiency, about 
.6 watt per candle power. 

The manufacture of the modern incandescent lamp is 
a science in itself, the high voltage, high efficiency lamp 
of today has only been perfected by means of hard and 
costly experiments. 

To obtain the best results from any incandescent lamp, 
it should be run at the exact voltage for which it was 
made. The filament in a high efficiency lamp at its cor- 
rect voltage, is heated as hot as it is safe to go without 



TYPES OF INCANDESCENT I,AMPS. II9 

andvLTy shortening the life of the lamps, and a rise of 
three or four volts on a no volt lamp is enough to short- 
en the life of the lamp 100 hours or more. 

As a general rule, a low efficiency lamp may be run on 
a voltage higher than that for which it was designed 
with less injury than a high efficiency lamp. 

In all lamps there will be noticed a ''blackening'* of 
the bulb, after having run the lamp for some time. The 
cause of this blackening of the inside of the bulb, is the 
basis of several different theories. It is known that it is 
a thin layer of carbon which is deposited evenly over the 
entire inner surface of the bulb and it is undoubtedly 
dependent on the make and grade of filament, and also, 
on whether the lamp is a * 'vacuum" or a "gas" lamp, it 
being claimed that gas lamps do not blacken nearly as 
fast as the usual vacuum lamp. 

The * 'series" incandescent lamp contains a filament 
which usually carries a much larger amount of current 
than the lamps used on constant potential circuits. In an 
incandescent lamp designed to run on a ten ampere con- 
stant current circuit, the filament will be quite large and 
if it be a * 'three watt' ' lamp, the voltage at the terminals 
of such a lamp, when giving 16 candle power, will be 
but 4.8 volts or in a 32 candle power lamp, the voltage 
(vould be 9.6 volts. On a four ampere lamp of 16 candle 
power, the voltage would be 12 volts, or 24 volts on a 32 
candle power lamp. The lamps would be connected in 
series of the manner arc lamps are connected. Owing to 
the danger of handling such series incandescent lamps, 
they have not been generally introduced for operation 
on arc circuits, but we find that in America, large num- 
bers of such series lamps are used for street lighting 



I20 TYPES OF* INCANDESCENT I,AMPS. 

from alternating current dynamos generating looo or 
2000 volts constant potential. 

In this case, the lamps will be connected in circuits 
of 40 or 50 lamps each, the lamps are connected in series, 
and each of these circuits is connected across the high volt- 
age mains. A three watt per candle power incandescent 
lamp will give about 250 candle power per electrical 
horse power. A four watt lamp will give about 185. 
An arc lamp will give at its nominal rating, about 
3000 candle power from' the same number of watts (746). 

Were it not for the fact that the intensity of light given 
out from a given source of illumination, varies with the 
square of the distance from the li^ht, the arc lamp would 
practically occupy the entire field, but the sub-division 
of light which is possible with the incandescent lamp, 
often gives a stronger light than the sam? energy used in 
arc lamps, in other words, ten 16 candle power lamps 
properly distributed, will often give a much better gen- 
eral illumination than one 2000 candle power lamp. 



TRANSMISSION OF POWER. 121 



CHAPTER IX. 



DIRECT AND AI.TERNATING CURRENT MOTORS. 



The transmission of power by electricity is the most 
efficient means of transmission for distances of any men- 
tion and is displacing steam, compressed air and water 
power to a marked extent. The losses in these several 
systems is enormous, but electricity of late years is trans- 
mitted great distances with but small loss. Generators, 
such as have been described, send current over distribut- 
ing wires which is utilized by machines called motors, in 
producing mechanical power. 

The object of the electric motor is to convert electricity 
into mechanical or motive power. The electric motor, 
in form and figure closely resembles and in some cases is 
identical with the dynamo, and all improvement in de- 
sign used to make an efficient dynamo, must be followed 
in motor construction, to obtain the best results. 

An electric current traversing a wire near a magnetic 
needle will deflect it to position at right angles to the 
flow of current or, a magnet free to move in a magnetic 
field will tend to set itself in the direction of the lines of 
force. 

A coil of wire carrying a current is pulled around in 
the direction of the lines of force when free to move in a 
magnetic field. 

In figure 34, a simple form of an electric motor is 
shown. The current enters the armature by the brushes 



12^ 



TRANSMISSION OF POWER. 



which are in contact with a two part commutator, and 
then passes around the armature coil. The signs -f" ^^^ 
— , indicating direction of current, as -|- is current enter- 
ing and — current leaving. 

The field magnets are shown marked N and S. The 
north pole N attracts the magnet of the south pole of 
the armature S, and the south pole S of the magnet 
attracts the north pole N, of the armature. For this 
reason motion will be given the armature. As the arma* 
ture nears the position in which the attractive force 
would have been satisfied, the commutator segments, 
which are also revolving with the armature, have reached 




FIGURE 34.— KLECTRIC MOTOR. 

a position where the segment which had previously been 
in contact with the + brush, has now moved so as to be 
in contact with the — brush, and the opposite segment is 
now in contact with the + brush. 

This must reverse the current in the armature and also 
the magnetism and the result is that the armature again 
revolves one-half revolution. This action continues and 
gives continuous rotation. Such an armature would 
have a **dead centre" which is of course obviated by 
placing more coils on the armature. The * 'torque' * or 



TRANSMISSION OF POWER. 12$ 

tendency to revolve, will of course depend on the amount 
of magnetism in the armature and field magnets, and this 
of course will depend on the current supplied. 

The principle of electric motors applied years ago, con- 
sisted in energizing electro-magnets by a suitable battery 
current, and by the attraction of their magnetic poles, 
producing mechanical motion of a rotary nature. Later 
an armature of the Gramme type was placed between 
permanent magnets and current supplied, which pro- 
duced rotation. It was noticed that by applying motion 
to the armature, electric currents were produced and 
that applying currents to the armature, motion or power 
was produced. The battery current, at that early period, 
was found to be unsteady, because soon exhausted and 
was expensive to maintain. Soon after current from 
dynamos were supplied to motors at greater economy. 

Following this stage of development, it was found that 
the dynamo could be used as a motor, when supplied 
with suitable current, and the motor as a d3mamo, when 
supplied with power or motion. 

In other chapters, the dynamo was described as gener- 
ating electric currents by applying mechanical force to 
rotate the armature. The electric motor is the converse 
of the dynamo, inasmuch as the motor generates mechan- 
ical power by applying electric currents to the machine. 
Dynamos, when supplied with proper currents run as 
motors, but not always with efficiency. Commercial 
motors operate exactly as the one previously described, 
but as this type would not be efficient, it serves only to 
illustrate the actions in the motor. All commercial 
motors have a field winding which, when current is passed 
through it, gives a poweiful magnetic field. The arma- 



124 TRANSMISSION OF POWER. 

tures are composed of many coils of wire, instead of one. 
as in the figure, and for this reason no * 'dead centre" will 
result. The following statement known as Lenz^s law 
is applied to dynamos. ''The reaction of an induced cur- 
rent generated by the mechanical movement of a conduc- 
tor, is always in opposition to the movement" ; hence the 
currents induced in the armature of a dynamo react ic 
opposition to its rotary movement. As explained in an- 
other chapter, the power required to drive a dynamo is 
simply enough to overcome this action, and as the cur- 
rents are increased or diminished, the engine must exert 
more or less power by connecting a dynamo already rim- 
ning to another which is to run as a motor, current is 
thus supplied and produces a force tending to revolve 
the armature, and if no mechanical force is present to 
oppose, the armature of motor starts to rotate. 

It ought to present itself quite plain to the reader that 
as the motor armature is turning in its magnetic field, 
there must be a tendency for current to be generated in 
the coils, depending on the magnetism, speed, etc., as in 
the dynamo. Now it is found that when a motor is 
started up, connected to a constant potential circuit, that 
it takes a large current from the supply wnres and as the 
speed increases, the current diminishes. The resistance 
of the armature is very low and from first thought, we 
would suppose that large currents would be required as 
the speed increased. But as the current decreases on the 
circuit as speed increases, the impression is left that there 
must be a resistance acting in the armature. 

In the dynamo, powxr is applied to the armature to 
produce current, but the production of current tends to 
stop the motion given the armature. 



TRANSMISSION uF POWER. I25 

Current is applied to the motor to produce power, but 
the motors own dynamo action as the speed increases, 
tends to diminish the current applied. 

This Electro Motive Force, or counter K. M. F. is pro- 
portional to the speed, and acts as a governor, which 
holds back the current to the motor, but as the motor is 
called on to do more work, the speed is lessened, the 
counter B. M. F. is decreased and the current from dyna- 
mo is increased and forced through the motor creating 
a greater torque. 

Si. ppose a number of storage batteries and a dynamo 
are connected in multiple and both are supplying current 
to feeders. While the batteries maintain the same E. M. 
F. as the dynamo, current will flow to the feeder from 
each, but iftheE. M. F. of batteries should fall below 
dynamo pressure, current will flow from the dynamo to 
the batteries, opposing them, and a quantity of current 
supplied the feeder will depend on the pressures of the 
dynamo and storage battery. The existence of a counter 
E. M. F. is absolutely necessary. The higher the coun- 
ter E. M. F., of a motor of given size, the higher its 
efficiency will be. 

Motors are usually built so as to give the best results 
at certain speeds and voltages, and as a rule a greater or 
less voltage supplied will lower the efficiency. 

Motors for direct current work are distinguished by 
the manner of winding the field magnets, into series, 
shunt and compound or differentially wound motors. 

The series motors on constant potential circuits, are 
used mostly for street car work and other places where 
a strong starting torque is demanded. Small fan motors 
are generally series wound. 



126 TRANSMISSION OF POWER. 

Shunt or compound wound motors are used for station- 
ary work, and their speed can be made practically con- 
stant, when supplied with a constant potential current. 

Alternating current motors are being rapidly intro- 
duced in America and are designed to operate in most 
cases, on multiphase currents. Single phase motors are 
usually of the syncronous type, the dynamo current 
being supplied to the armature windings, but many of 
the two and three phase motors are designed so that the 
dynamo currents passing through the field magnet wind- 
ings only, which produce effects tending to rotate an ar- 
mature whose conductors are of the most simple form and 
have no external connections. These are known as 
"induction" motors, and the Telsa motors so well known 
are generally of this type. 

During the past few years great strides have been mide 
toward perfecting alternating current motors to be used 
for transmission of power. 

The alternating current alone is capable of performing 
this work in a satisfactory manner, when the amount of 
power is large and the distance great. The great flexi- 
bility of the system is easily seen. By means of an alter- 
nating current loo H. P. generator of 500 or 1000 volts 
potential, alternating current may be supplied to a ''step 
up'* transformer, which may raise the pressure to 10,000 
volts and transmit it 25 or 30 miles, where it is then re- 
duced in pressure, to the low voltages used in the motors. 
The relative amounts of copper used in a 1000 volt and a 
10,000 volt distribution for a given distance will be 100 
to I, the relative amount of copper used in a given trans- 
mission varying inversely as the square of the potential 
at which it is distributed. It should be possible, in an 



TRANSMISSION OF POWER. I27 

alternating current power transmission, to obtain from 
50% to 95% of the energy given the generator at the dis- 
tributing or motor end of the line, the per cent varying 
with the conditions. 

It is a vastly different problem to build a direct cur- 
rent transmission plant using 10,000 volts pressure. In 
the first place the dynamos would be practically impossi- 
ble to build, if of any large size, for the problem of insu- 
lation of dynamo and motor and their commutators 
would be most difficult. Transformers, however, may be 
easily constructed which will withstand this high pres- 
sure, and by means of **step up" and **step down" trans- 
formers, the dynamos and motors need not be subjected 
to but a low voltage and they would for this reason, be a 
much safer and more satisfactory apparatus. 

In the synchronous motor, operation is obtained as 
follows: the motor being simply an alternator reversed. 
The motor is brought up to the speed of the generator 
by means of a small starting motor and when the motor 
is in step with the generator, as indicated by the syn- 
chronizer, the switch is thrown, connecting each to each. 
These machines run very smoothly and stand considera- 
ble overloading, when they will pull out of step and stop. 

The multiphase motor usually has a closed coil short 
circuited armature, with no rings or commutators. The 
windings of the field of the Telsa alternating current mo- 
tor consists of two circuits traversed by a two phase cur- 
rent of different phases, usually 90° apart, and currents 
of low potential, are thus induced in the armature, which 
react on the fields, causing continuous rotation. This 
type of motor is also called the * 'rotary field" motor, 
owing to the rotating magnetic field generated by the 



128 TRANSMISSION OF POWER 

two phase currents in the field windings. The large mo- 
tors are built on the same plan with windings somewhat 
altered. These machines start up with great torque on 
heavy loads. 

The general application of the direct current electric 
motor to street railways, has been almost phenomenal. The 
first electric railway was first put in operation early in the 
year 1888 on the Sprague Road at Richmond, Va. 

There had before this time been many experiments made, 
but this road is probably the fiirst one on which the principles 
now in use were introduced. 

The usual car equipment consists of two motors and regu - 
lating devices for regulating their speed. 

The street railway motor is universally a series wound 
motor, for, considering the requirements of this work 
the series wound motor possesses more points of advantage 
than other types. The motors are supplied in probably 
99 per cent of American railways with a constant potential 
current of about 500 volts pressure. Notwithstanding many 
newspaper articles in regard to the * 'deadly trolley" there 
has yet to be a case reported of an able bodied man 
being killed or even permanently injured by, a shock of 
500 volts. Both of the authors of this book would now 
have been * 'planted" several times over, if a 500 or 550 
volt shock were fatal. 

This uniform agreement on 500 volts as a standard 
pressure, is practically decided on by all the manufactur- 
ers of electric railway apparatus, as a pressure which is 
not dangerous to life but is as high as is safe to go when 
difficulties of insulation are considered in both dynamo 



TRANSMISSION OF POWER. 1 29 

and motor construction. The street car motors are often 
wet and are exposed to a great deal of dust and dirt, and 
the subject of insulation under these circumstances, is a 
very perplexing one. Were it not for the extra cost of 
copper in distributing the current, there is no doubt 
but that the 500 volt plan of current distribution would 
be changed to one of lower voltage. The vast majority 
of electric roads use the overhead trolley system of cur- 
rent distribution, and as been previously described, the 
rails are bonded and should constitute the return circuit, 
although often being aided by the low ground resistance. 

The conduit systems of electric railways, which consist 
in placing the conducting wires in conduits under the 
surface of the street, are now being investigated in Amer- 
ica, and it is to be hoped that a simple and reliable sys- 
tem of this kind will be devised to furnish means for 
operating cars in large cities, where the trolley is objec- 
tionable. 

Storage batteries have been tried in many places for 
operating street cars, and with a few exceptions, have 
not proved satisfactorv. 

The reasons are many, and some of them are inherent to 
the system. The storage battery of to-day weighs from 
60 to 150 lbs. per H. P. capacity and on a car which may 
require a considerable power in climbing grades, etc. the 
batteries are usually a very heavy load, several times in 
fact, that of motors and equipment of a well designed 
trolley car. 

The batteries are likely to be over-loaded and this re- 
sults in a reduced efficiency. The net efficiency of the 
best storage battery system will probably be from 5 % to 
15% less than a first class trolley system. Some of 



130 TRANSMISSION OF POWE:r, 

these defects of storage batteries will be shown in a suc- 
ceeding chapter. 

There would certainly be many advantages in having 
a storage battery system of street railways and this should 
be a practical and commercial process, were it not for the 
excessive weight in comparison to the output. Bach car 
would be independent of the power house when on the 
road, and the methods of speed regulation of the motors 
may be accomplished in a most practical and efficient 
manner, by varying Ihe number of batteries connected to 
the motors, and thus vary the voltage applied, and thus 
the speed. 

The usual series motor for street car work, operating 
on a 500 volt constant potential circuit, may be regulated 
usually by one of two ways. The first plan is to have the 
field magnet windings divided into a number of coils, and 
these coils which may be connected in several relations to 
each other, are connected in series with the armature. 

By varying the strength of the field magnets by chang- 
ing the field connections, it is possible to get several dif- 
ferent rates of speed. The Bdison-Sprague street car 
motors are wound in this way and by means of a con- 
troller switch, the motorman simply varies the connect- 
ions of the field coil sections, which is done by a partial 
revolution of an insulating cylinder on which are mount- 
ed metal conducting strips which, being against the mo- 
tor connections, place the terminals leading from the 
motors, in various combinations with each other. The 
usual Sprague-Kdison equipment of recent design, as 
furnished by the General Electric Co., has a controller 
stand or starting switch that has seven different combin- 



TRANSMISSION OF POWER. 



13^ 



ations in bringing the car from rest to full speed. The 
field coil is divided into three sections, each of about 
equal resistance a, b and c, figure 35. 

The connections on the various points are sho^Yn plain- 
ly in the diagram numbered from i to 7. 
j On the movement of the switch handle from ''off*' to 
one, the combination of connections as shown in diagram 
•^PJVVGUE -EDISOK -CONNBICTIOKS • 



;rwpi.tfr 



I^H- 



r> — i— AV-^2RP-^^ZP— ^(^ 






Gf 



TV 



-W—'B^-'W (2>- 



T^— ^ 



T>- 






■<£>- 



-©- 



■^m 



-<o>- 



<2y 



<2>- 



N9^ 2 • 4 • 7 • A^e THe 

PE5T RUNMING POlftTS- 
FIGURE 35. — SPRAGUK-EDISON STREET CAR MOTOR 
CONNECTIONS. 

one, is made with each motor under the car. The resis- 
tance, Rh., is placed in series with the field coils, a, b 
and c, which are in series with themselves and with the 
armature M. The resistance is used in starting the mo- 
tors, for when the motors are standing still and not pro- 
ducing any counter B. M. F., they would otherwise allow 
a large rush of current to take place when they were first 
started. 

On the second position this resistance is removed, but 



132 TRANSMISSION OI^ POWER. 

the coils a, b and c, and the armature are still in series 
relation to each other. The coil a, of the field is now 
short circuited 3, and in position 4 it is placed in multi- 
ple with coil b, thus coils b and c in multiple, are now in 
series with coil c and the armature. Point 5, short cir- 
cuits the coil c, which is then cut out of circuit entirely on 
point 6, thus leaving coils a and b in multiple to furnish 
the magnetism of the fields. In point 7, the three coils 
a, b and c are placed, in multiple with each other and in 
series with the armature, and this furnishes the weakest 
field, and the path of lowest resistance to the flow of cur- 
rent. The motor on this point is exerting its maximum 
power. Points 2, 4 and 7 are the best • 'running points'*, 
and in operating this system, these points should be used 
in preference to others. In handling the starting switch 
all movements should be firm and steady. If a point is 
partially passed, move the handle to the next point, 
never stop between points. In starting a car, let the car 
start to move on the first point before moving to the 
second and thus prevent the heavy rush of current which 
would take place. 

The other method of motor control which is in general 
use, is by means of a variable resistance placed in series 
with the motor, the fields of which are always in series 
with the armature and the relations of the coils are not 
varied except after all the resistance has been cut out of 
circuit, when the field strength is sometimes weakened 
by cutting out or short circuiting a section of the field 
coil, which must of course raise the speed to the maxi- 
mum. Except at the point at which all resistance is cut 
out, the efficiency of this method is not usuallyas high 
as in the commutated field method of regulation, but the 



TRANSMISSION OF POWER. I33 

simplicity of the plan is such as to largely overcome this 
objection, and this plan is used by Thomson-Houston Co. 
on most of their equipments. The Westinghouse Co. 
use practically the same methods of motor control on 
their usual street railway apparatus. 

There has lately been revived a method of series multi- 
ple connection of motors, which is now being adopted by 
roads on account of its economy. The motors are two in 
number, as usual in American street car practice, and 
they are adapted to be connected in series on starting the 
motors, which placed 250 volts on each motor. With 
this manner of connections, the motors will operate very 
economically at low speeds, such as would be used in 
going through crowded streets of large cities. When a 
higher speed is required, the motors are placed in multi- 
ple on the 500 volt lines and the motors at once run at a 
much increased speed. In this method of motor control, 
the fields are sometimes divided in sections, or as in the 
usual type of Westinghouse Series multiple controller, 
the entire changes are affected by varying the connec- 
tions of the motors and a resistance placed in series with 
them. 

A later method of motor regulation as used by the 
General Electric Co., consists of a resistance adapted to 
be placed in shunt or parallel with the series field coils, 
when maximum speed is desired. This shunt resistance 
of course robs the fields of part of their current, and 
weakens them and thus increases the armature speed. 
The plan of series multiple connections of the General 
Electric Co., is shown in figure 36, in which i and 2 rep- 
resent the two motors under the car. 

The connections as made by the movement of the con- 



i34 



TRANSMISSION OF POWER. 



troUer switch, are shown starting with the *'off" point, 
and ending with the two motors in multiple on full line 
pressure with the field windings shunted by means of the 
resistance Ri and R2, and thus running at their highest 
speed. In starting on first point, the resistance Rhi and 
Rb2, is placed in series with the motors which are in 
series relation to each other. 

^£R1E.^ -nt)lTrPL£ ' CONNECTIONS r 
T v-4— A/VA/V— <i^-^3M^-^-A(^ — ©-^oTRnp — ^' 

t i-t—\N <i>-^m^ — V\/ (^—ws^ — et- 



t^^ 






<£>-w^r — 0' 



t^ 









poiKTS 5 • 7 • ARE ^.9'f fttjsMiMa P01M6 




— & 



e^-^WT^ 






Ia/VW\AIb,4' 



ff- 



FIGURE 36 — SERIES MUI,TIPI.E STREET CAR MOTOR 
CONNECTIONS. 

On the second point, }i of the resistance Rhi and RI12I 
is cut out and on the third point, all the resistance in 
series with the motors is removed, and on the fourth point 
the field coils are shunted by the resistance Ri and R2. 
The points 5, 6 and 7, are not running points and are not 
marked on top of the controller box or stand. During 
these points, the motors are being changed from series to 



TRANSMISSION OF POWER. I35 

parallel relation, as shown in point 8, and from this to 
the maximum speed point at number 10. 

Motors are known in types, as ^^gearless", * 'single 
reduction" and ^'double reduction", owing to the various 
methods of connecting the revolving armature to the car 
axles. A gearless motor is mounted on the axle usually, 
except in one case where a single large motor is con- 
nected to the two car wheels by means of connecting 
rods, such as are used on locomotives. The gearless and 
single reduction type of motor has been brought out 
within the last year or so and to-day the majority of roads 
use the double reduction motors, which although noisy 
and necessitating large repairs on the double set of gear- 
ing, are usually of light weight for the power developed 
and are, if anything, more efficient than the heavier 
slower speed motors. 

The single reduction motors of various makes do away 
to a large extent with the gearing repairs and seem to 
be the most desirable for the usual street car service. 
These motors are not excessively heavy and are as a gen- 
eral rule more efficient than the gearless types. 

For high speed service, the problem is somewhat dif- 
ferent and the gearless motors should be well adapted to 
this service, for the armature speed would be high and 
the motor quite efficient. Owing to a lack of room under 
a car for motors, gearless motors are difficult to build of 
sufficient power and efficiency that will go in the limited 
space allowed. 

It should be remembered in this connection, that the 
high speed motor is a much lighter motor for a given 
power than a slower speed motor. Thus as the armature 
speed is reduced, the magnetic field must be increased in 



136 TRANSMISSION OF POWKR. 

strength or the armature coils must be increased in size 
and number, which means a heavier motor. 

Street car motor repairs are often heavy and expensive 
and in many cases are due to careless handling. The 
usual street car motor of any make or type is always 
working under disadvantages compared to stationary 
motors protected from the weather. The street car motor 
is exposed to dust and dirt in dry weather, and water and 
mud in wet weather, and owing to the high pressure 
used, 500 volts, it is often most diflBicult to keep armature 
and fields from grounding and thus disabling them. The 
frames of the motors are of course connected to the metal 
car trucks, which are grounded, and in wet weather 
water or mud may ground or short circuit the fields or 
armature of the motors. 

"Bucking" is the usual name given to a violent jerk 
which often takes place when a motor is grounded. Its act- 
ion is very much like that of a "bucking bronco" and may 
strip the cogs from the gears or shake up the passengers 
badly, depending on its severity. If a motor is running 
at full speed and a ground occurs on the wire between 
the fields and the armature of the motor, the fields are 
often made to carry a much greater amount of current 
than they should. The armature at once begins to act as 
a generator and ' 'bucks' ' . A flash from brush to brush 
across the commutator will often cause the same effect. 
In case of trouble of this kind, look for a grounded field 
or brush terminal. If the motor is permanently ground- 
ed, cut it out and proceed to the barns with one motor. 
The brushes and commutator of a motor should receive 
excellent care. In case of sparking-, see that your brushes 
axe being pressed against the commutator firmly by the 



TRANSMISSION OF POWER. 137 

springiL and that they are properly fitted to the commuta- 
tor surface. Copper coated carbon brushes are superior 
to those not coppered, for they heat less. 

Never reverse a car when running if it can be possibly 
avoided, and then it should be done in a moderate man- 
ner or the fuse is likely to ''blow" or the cogs to break, 
and thus effectually stop all chances of stopping suddenly 
in this way. In going down grades it is bad policy 
to run at an excessive speed, experience having shown 
that several of the worst accidents which have ever 
occurred on electric railways, were caused by run-away 
cars on grades. The series multiple controller or start- 
ing switches are provided in some cases with a locking 
switch, which prevents a motor being reversed while cur- 
rent is on the motors. In climbing grades, always run 
on one of the ''best running points", and thus avoid any 
possible damage from overheating field and armature 
coils. On a slippery rail, care must be used in starting, 
to avoid slipping. A moderate use of sand is recommen- 
ded and in case wheels slip as speed increases, move 
starting handle back and throw on current again gradu- 
ally. Go slowly around curves, for your trolley is not 
only likely to jump off the wire, but broken and dam- 
aged trucks are often the result of such reckless running. 
The trolley pole is also likely to break span wires, etc. , 
of the trolley line. 

A motorman should never leave the car without first 
removing the starting handle from starting box. 

Motor cars, if properly designed, should be able to 
mount grades of 15% to 18% and several roads in Amer- 
ica are operating daily on grades of 13% and over. 

Incandescent lamps in street cars are usually connected 



138 TRANSMISSION OF POWER. 

SO as to place five 100 volt lamps in series. Some cars have 
one set and others two, and as a general rule electric cars 
are the best lighted of any cars used for passenger trans- 
portation in the country. Incandescent lamps, when 
placed in series, should always be of '.he same make and 
candle power, to give the best results. Lamps should 
not be allow^ed to become loose in their sockets, for 
socket repairs are sure to follow. 



STORAGE BATTERIES. I39 



CHAPTER X. 



STORAGE BATTERIES. 



Electricity passing through a liquid solution from one 
metal plate to another will produce chemical action. 
The action will depend on the quantity of current used, 
the kind of solution and the material of which the plates 
are made. 

The history of the storage battery or * electrical accu- 
mulator" dates back to 1 801, when one of the scientists 
of the day noticed that if two plates of the same metal 
were immersed in an acid solution and current be passed 
from one plate to the other, that after they had been dis- 
connected, electric currents could be obtained from 
the plates by connecting them together by a conductor, 
the current flowing in an opposite direction to that o\ 
the current with which the **cell" had been charged. 

No material progress seems to have been made from 
this date until 1859, when Planted, while experimenting 
in this line, made a storage battery consisting of sheets 
of lead immersed in a solution of dilute sulphuric acid. 
He found that w^hen currents of electricity were passed 
though the solution from one plate to the other, that a 
chemical action was at once set up, tending to change 
the chemical composition of the lead plates, one of which 
being connected to the positive pole of a primary battery 
would gradually assume a reddish color and the other 



I40 STORAGE BATTERIES. 

remaining practically unchanged. He found that after 
current had been sent through the battery, that it would 
exert a counter Electro Motive Force, (counter K. M. F.) 
of from 2 to 2.5 volts and that in discharging the cell, 
that it would show an B. M. F. of about two volts until 
there had been given back from the cell nearly the amount 
of current used iu charging it. He also found that by 
charging a cell and then discharging it, and then revers- 
ing the cell and charging it in the opposite direction that 
its storage capacity would be increased to a large extent, 
and this process of **forming" the plates w^as always gone 
through until the plates became porous and would hold 
a charge of many times what they would at first. This 
forming was necessarily a long, tedious and expensive 
operation, and some time later it was discovered by 
Faure, that if a paste made of oxide of lead be supplied 
to a lead supporting plate, called a * 'grid' ' that the pro- 
cess of forming was so shortened as to be practically 
done away with. It also made it possible to reduce the 
weight of the plates to a great extent and the majority of 
electrical accumulators or storage batteries used m Amer- 
ica are now made on this plan. 

It will be evident that it will be necessary in any bat- 
tery to provide means for keeping the positive and neg- 
ative plates from touching each other, and thus short 
circuiting. Various methods have been tried, a few of 
which will be mentioned. Hard rubber * 'combs'* or 
**hair pins" may be placed on the plates and thus keep 
them separated from each other. In one type of battery 
using pasted plates and "grids'' for supporting the active 
material, plugs of active material in the negative plates 
are removed in certain places in the plate and rubber 



STORAGE BATTe:RIES. 



14 X 




FIGURE 37. — STORAGE BATTERY PIRATES. 
PASTED PLATE TYPE. 

plugs are placed in these openings so as to hold the posi- 
tive plates away. In other cases a perforated hard rub- 
ber plate or a sheet of asbestos paper is placed between 
the plates. Owing to the * 'buckling" of the lead plates, 
it is often a very difficult matter to keep the plates apart, 



142 STORAGE BATTERIES. 

and in case of contact, the cell will at once become dis- 
charged and very likely injured. A deposit of active 
material often forms at the bottom of the retaining cell 
and unless the plates are raised some distance from the 
bottom of the cell, trouble may arise from a short circuit 
at this point. 

It should be understood that no matter how large a 
single storage cell, either of the Plante'' or Faure type 
may be, or how many plates it may contain, that its volt- 
age will never be higher than from 2 to 2.5 volts. The 
* 'ampere hour" capacity will vary however, with the size 
and number of plates exposed to the solution, and to get 
a voltage of say, 100 volts, it will always be necessary to 
connect at least 50 coils of battery in series, each cell 
having about two volts B. M. F. There is always a max- 
imum charging rate for a given size plate, which should 
never be exceeded. A plate when being supplied with 
more than this rate will be likely to be injured by warp- 
ing or by being "buckled" as this bending or warping of 
the plates in called. The cells are rated on their ' 'ampere 
hour capacity" and each size of cell with its ''elements" 
will have a rate at which it may be charged and dis- 
charged giving its maximum elB&ciency. A well known 
make of storage battery of 150 ampere hour capacity, 
may be described as as follows: — voltage about two 
volts — number of plates 23, 11 of which are positive and 
12 negative, thus giving each of the positive plates a neg- 
ative plate either side of it. The size of both positive and 
negative plates are the same, i2X6X}i inches thick. 
The normal charging rate is about 25 amperes and the 
discharge rate from 25 to 30 amperes. The weight of 
cell and liquid complete is about 45 pounds. 






STORAGE BATTERIES. 1 43 

The discharge rate may be slightly increased, but the 
capacity of the cell will be diminished to a considerable 
extent. 

We have stated that the large number of American 
made storage batteries are manufactured on the * 'pasted 
plate" or Faure principle, but of late many cells of the 
Plants' type are being used in America. The mechanical 
construction however, of the plates is very different from 
the original Plante^ battery. 

In one leading make of the Plante^ type of battery, the 
plates are formed of lead ribbon whose surface has been 
previously roughened, the ribbons being about ^ to ^ 
inches wide and placed in a horizontal position between 
heavy lead end supports. The plate really consists of a 
large number of thin lead strips, piled one over another 
until the plate when complete measures in the medium 
sizes about 6xSX/4 inches thick. A number of such 
plates are then connected by means of lead lugs on the 
heavy frame of the plates, and in this way a completed 
cell is put together, and the plates are now ready for 
* 'forming". This is done in the usual manner, the per- 
Dxide of lead formed from the ribbons fills up the spaces 
between them and at last forms a practically solid plate 
of **active material" as the peroxide of lead is called. 
There is always supposed to be enough of the lead ribbon 
left to form a support for the active material and when 
such batteries are properly cared for, they should give 
good results. They will stand a heavy discharge with- 
out buckling and will withstand considerable hard usage 
such as is experienced in train lighting, etc. 

The positive and negative plates of lead batteries, may 
be easily distinguished by their color, the positive plates 



144 STORAGE BATTERIES. 

being of a reddish color and the "negatives" of a metallic 
lead color. When in good condition and fully charged, 
the * 'positives" should be of a dark plum color. 

The solution of sulphuric acid and water in the plates 
are immersed will be found to vary in its specific gravity 
with the charge in the cell. When the cells are com- 
pletely discharged, its specific gravity should be from 
1. 15 to 1. 16 and when fully charged, its specific gravity 
will be somewhat greater. The mixture is about ^q acid 
and 1% water and* should be tested after mixing with a 
hydrometer, which gives the specific gravity. The solu- 
tion evaporates rapidly when in a cell which is in actual 
service and w^ater should be added to keep the solution 
right. If the solution does not contain enough acid, pour 
in solution already mixed and never pour clear acid in on 
the plates to increase the specific gravity of the solution. 

In charging storage batteries, the positive terminal of 
the dynamo should be connected to the positive terminal 
of the series of cells. 

In charging the usual lead storage battery, it will be 
found that until the batteries are almost charged, 
the electro motive force of each cell will be from 2 to 2. i 
volts, but as the charging progresses, the voltage may rise 
as high as 2.3 volts, but when the charging current is 
stopped, the voltage falls to about two volts. A low 
reading voltmeter should be used in testing storage bat- 
teries and the terminal reading of a single cell is usually 
a correct showing of the condition of the cell. If it is 
found that a single cell tests lower than the others in 
series with it, the cell should be removed and exam- 
ined. It may be found that the plates are buckled and 
in this case they must be straightened again by mechani- 
cal means. 



STORAGE BATTERIES. 145 

The negative plates as a general rule, do not need 
renewals, but the positive plates are often subject to 
repairs which cost at least io% per annum of the original 
cost of the cell. In many cases of train lighting, the 
positive plates last but a year on an average, but this 
service is very severe. 

The connections between the batteries and in fact, all 
corrodible parts of the battery plant should be liberally 
treated with asphalt paint. All connections should be 
made in a strong and servicable manner and unusual 
care taken in insulating all parts of a battery which is to 
be charged from a high voltage constant cuirent circuit. 
When charging from a constant potential circuit, a resis- 
tance is usually put in series with a set of cells, so as to 
keep the charging current uniform. 

An automatic safety cutout should also be provided, so 
as to cut out the batteries in case of a dynamo being 
stopped w^hile connected to the storage batteries, for if 
this was not done, the dynamo would be supplied with 
current and run as a motor. A shunt wound dynamo is 
better adapted to storage battery charging, than the 
series wound dynamo for several reasons one reason 
being, that it is not easily reversed by failure of cutouts 
working, etc. 

Although we have spoken of the lead type of stor- 
age battery only, there are several other types which are 
worthy of considerable study. One of these is called the 
* 'alkaline' ' accumulator, and has for its positive plates, a 
mass of finely divided copper surrounded by a copper 
wire gauze which holds the copper in position. The 
plates are then placed in an iron containing cell, which 
is so constructed that iron partitions come between the 



146 STORAGE BATTERIES. 

positive plates, but are held away from them. The solu- 
tion used is one in which potash is dissolved and before 
the cell is ready for use, a quantity of zinc is dissolved in 
the solution and held in suspension in it. When the 
battery is charged, the zinc is deposited on the iron case 
and partitions between the positive plates, and the cop- 
per in the positive plates is oxydized and the electro 
motive force of the cell will be found to be about ^q volts, 
much lower than the lead types of battery. When the 
cell is discharged, the copper oxide is reduced and the 
zinc on the iron partitions is again dissolved in the pot- 
ash solution. Although the voltage of the cell is low, its 
current capacity is high and a cell capable of furnishing 
about 300 watt hours, w^ill weigh but }4 as much as the 
usual lead cell. The K. M. F. of this type of cell is quite 
constant and owing to its small weight and size as com- 
pared to the same capacity of lead cell, its application to 
street car propulsion is to be watched with interest. 

The Edison storage battery has recently appeared as a com- 
mercial article. Its chief advantage over the lead cell is that 
it is light and compact and may readily be adapted to traction 
work. The jar in which the elements are retained is made of 
nickel plated sheet steel. The electrolyte is a 21 per cent solu- 
tion of potassium hydroxide. The negative plate consists of 
iron oxide contained in small receptacles on a metal plate, and 
the positive plate consists of nickel hydrate contained in small 
steel tubes held together by a steel frame work. On first 
charging, the iron oxide is broken up ; the oxygen uniting with 
the nickel hydrate of the positive plate, forming a higher 
oxide of nickel. On discharging the reverse is true, that is, the 
nickel oxide is changed to a lower oxide ; the oxygen uniting 
with the iron oxide of the negative plate. The voltage is 1.5 
volts, and the Edison cell with the same watt hour capacity 
weighs one half as much as a lead cell. 



STORAGE BATTERIES. I47 

Storage batteries cannot be charged by means of the 
alternating current, a fact which is at once evident when 
it is remembered that with the current reversing its 
direction many times a second, a chemical action such as 
is necessary in any storage battery, would be out of the 
question. It will thus be seen that the storage battery of 
any type will always be used in connection with direct 
current stations, and their value is now becoming gener- 
ally known in America and Europe. There are many 
electric light stations supplying low pressure direct cur- 
rent for incandescent lamps, etc., in large cities where 
current must be supplied at all hours of the day or 
night. In such a station it will usually be found that 
during the brightest hours of the day and between mid- 
night and morning, that the load on the station is very 
light, so light in fact that the smallest dynamos and 
engines in the station may be under-loaded. 

We will find in many such cases as this, that a set of 
storage batteries may be installed and effect quite a sav- 
ing in the operating expenses of such a plant. During 
the hours of the day when the load is smallest, the stor- 
age batteries may be charged. Then as the heavy load 
comes during the early hours of the evening, the batter 
ies may be connected so as to help furnish current to the 
circuit and later after the load has lessened to the capac- 
ity of the battery, the engines and dynamos may be 
stopped, and the batteries will furnish the necessary 
current until morning, when the dynamos are started to 
carry the daily load. Thus the running hours of the 
station are not only shortened, but as the dyaamos, dur- 
ing the day, are carrying a load nearer their maximum, 
both the engines and dynamos should operate at a higher 



148 STORAGE BATTERI^. 

efficiency. By this means, a considerable saving can 
often be eflfected, and many central stations and office 
buildings having their own plants, are now using storage 
batteries to obtain these results. 

By means of the storage battery, a smaller dynamo 
may be made to furnish current for a much larger num- 
ber of lamps, for a limited time, than it would be able 
to carry alone. This is well illustrated in the electric 
lighting plants installed on some of the steam railroad 
trains in America. A dynamo, direct connected to a 
high speed steam engine has a maximum capacity of 
about 80 amperes at 70 to 80 volts pressure. The incan- 
descent lamps used are 16 candle power and are 
about 200 in number on a six car train and require 
about 150 amperes at 64 volts pressure. It will tbus be 
seen that the lamps on the train require 150 amperes of 
current of which the dynamo can supply but 80, when 
working at its full capacity, and since the engine drivino: 
the dynamo gets its supply of steam from the locomotive, 
it is often impossible to get any steam at all in certain 
sections of the road when all the steam in the boiler must 
be used to operate the locomotive in pulling the train. 
Thus it will be seen that to maintain a reliable light, a 
storage battery is the only means which can be used to 
obtain good results, under such conditions. In practice 
32 cells of 150 ampere hour batteries of the lead type, are 
generally placed under each car and their voltage w411 
thus be found to be about 64 volts for the set of 32 cells. 

The dynamo is run continuously, except at such 
times as the locomotive is disconnected or steam cannot 
be obtained for other reasons and in this way the batter- 



STORAGE BATTERIES 



149 



ies are always in condition to supply the current needed in 

addition to 
that from the 
dynamos. 

Train light- 
ing service is 
very severe 
and much time 
and money has 
been spent in 
developing 
practical and 
successful sys- 
tems of train 
lighting. 

Probably the 
greatest appli- 
cation of 
the storage 
battery — 
both the 
lead cell 
and the 
Edison cell 
— is to the 
elect ric 




Figure 38. — typical storaae battery. 



carnage. 

The car- 
riage is propelled by a small motor. The chief advantage of 
the application of electricity to the carriage is the ease with 
which the carriage may be controlled. 

By means of a set of storage batteries from the usual 
arc lighting circuits of constant current type, incandes- 
cent lamps may easily be operated on the usual multiple 
plan. This would hardly be an advisable thing to do 



I50 STORAGE BATTERIES. 

however, in residence lighting, unless an automatic 
device prevented the incandescent lamp circuit from 
being thrown on while the high voltage arc light circuit 
was charging the cells, for otherwise the handling of the 
sockets and incandescent lamps might be a dangerous 
thing to do. 

The storage battery has also been used to a large ex- 
tent for operating small motors in phonographs and 
other automatic machines. Their use in medical and 
surgical work is also quite general. 

The application of the storage battery to street railway 
work is at present far from general, but as suggested in 
previous chapter, the storage battery system is an ideal 
one and a fortune awaits the successful investigator in 
this line. 

A few points in regard to the care of the usual lead 
type of accumulator, in addition to those already men- 
tioned, may be of value to those charging or handling 
them. 

Storage battery plates are usually received from the 
makers after having been formed, and, after having 
placed the plates in position in their rubber or glass cells 
and having taken due care in seeing that the positive 
and negative plates do not come in contact with each 
other, they should be covered with acid solution of about 
1. 17 specific gravity and allowed to stand until the solu- 
tion has thoroughly entered the pores in the plates. 

The lead connecting lugs leading up from the positive 
and negative plates, should be painted with an asphalt 
paint to keep the acid from attacking the bolts and nuts 
usually used to connect one cell to another. Care should 
be taken to scrape the contact surfaces of the lugs and con- 



\ 



STORAGE BATTKRIKS. 151 

nectioiis between the cells, and thus reduce all ueedless 
resistance between the batteries. After a connection h^is 
been made, it should be painted with an acid and water 
proof paint or varnish, to prevent corrosion. The cells 
are connected in series. The positive plate of one cell 
connected to the negative plates of the next cell and so 
on. If the battery is to be charged from a constant 
potential circuit, care must be taken to allow but a safe 
amount of current to pass through the battery. The 
amount of current w411 depend on the counter K. M. F. 
of the cells and their resistance. Thus if we are to 
charge from a no volt circuit, we may safely charge from 
50 to 55 cells in series, each of the two volts K. M. F. 
A resistance should always be placed in series w^ith the 
set of batteries in such cases and in this way be varied to 
keep the charging current uniform. The amount of 
current that 1 10 volts will put through, say, 50 cells will 
depend of course on Ohms law. 

K 
C= — 

R 

But K or the number of volts, will be the difference 

between the counter B. M. F. of the set of batteries and 

the 1 10 volt circuit. Thus the voltage of the 50 cells 

may be 100 volts, in which case E=io or the difference 

between 100 and no. R or the resistance is likely very 

low, probably not over | ohm, and thus 

10 
C= — or 50 

1 
5 

which in a cell whose maximum charging rate is but 25 
or 30, will be too much. The only way to prevent this 
excessive flow of current, is to either add extra cells to 



152 STORAGE BA'TTERIES. 

the set or place a variable resistance in series with the 
set of batteries. The larger the size of the plates and the 
more their number in a s^iven cell, the lower its resis- 
tance will be. Knowing the charging and discharging 
rate of a given battery, and also its voltage and capacity 
in ampere hours, any problem in the application of the 
storage battery, may be worked out. New cells should 
receive several long and steady charges before being put 
on regular heavy work. The number of amperes multi- 
plied by the number of hours charged, will give the 
ampere hour charge and new plates after having been 
dried out in shipment, should be carefullv charged the 
first few times. 

- A cell should never be allowed to discharge lower than 
1.80 or 1.85 volts, and under no condition should a dis- 
charged cell be allowed to stand any length of time with- 
out recharging, for the plates are likely to become coated 
with a white coating of ''sulphate" which not only 
injures the plates, but can only be removed hy a most 
careful and tedious process of charging at a low rate. 

Buckled cells caused by short circuits or heavy charg- 
ing or discharging, should be taken apart and straight- 
ened by mechanical means. A heavy deposit of active 
material or *'mud" may be found in the bottom of a 
retaining cell and may be enough to short circuit the 
bottom of the plates. 

Rubber gloves should be used in handling the plates 
and solution, and woolen clothing should be w^orn, for 
cotton goods are soon destroyed by splashes of battery 
solution. Ammonia may be applied to discolored cloth 
and will often counteract the eflfect of the acid. 

Great care should be exercised in mixing the sulphuric 



STORAGE BATTERIES. 



^53 



acid and water. The acid should be poured in the water 
in small quantities and should be stirred well as it is 
being mixed. Considerable heat is always generated 
under such conditions, and the acid should be allowed to 
cool before passing over the battery plates. 



^ 



154 HEATING AND METAI, WORKING. 



CHAPTER XI. 



KI.ECTRIC HEATING AND METAI. WORKING. 



STATION INSTRUMENTS. 



Electric heating is a subject that at present is interest- 
ing many able workers in the electrical field. Its advan- 
tages over coal or gas for heating are many, and its 
only drawback is its cost when current at the usual 
lighting rates is used. 

The principle of all heaters both for direct and alter- 
nating current is that of passing current through resist- 
ing conductors which of course consumes energy and ex- 
hibits itself in heat. The conductors used in the usual 
heaters for electric street cars, are generally made of Ger- 
man silver or iron wires, and these wires are in most cases 
surrounded by some insulating material which is a good 
conductor of heat, such as fire clay, sand, or enamel c 
This material really furnishes the wire with a larger heat 
radiating capacity. It will be evident, for example, that 
if a heated wire is placed against a plate of cold glass 
that it will at once lower its temperature and gradually 
raise the temperature of the glass. The wire cannot in 
this case be raised to a dangerous temperature without 
passing through it several times the amount of current 
that would melt it in open air. The wires in the usual 
electric heater, thus carry a much greater amount of cur- 



HEATING AND METAI. WORKING. I55 

rent without being over-heated, than would be possible 
without the radiating material surrounding the wire. 

In one form of heater, the wires are fastened to an iron 
plate by means of enamel, the enamel not only complete- 
ly covering the wires and uniting them to the iron 
backing but also insulating them from the iron. The 
wire is in intimate contact with the iron plate by means 
of the enamel, and of course cannot become much hotter 
than the iron plates, which having considerable radiating 
surface, make efficient electric heaters. 

One of the earliest forms of electric heaters, patented 
in the United States, used iron or German silver wires 
imbedded in fire clay, the whole being incased in an iron 
box. This form of heater was used in the earliest elec- 
tric street railway put before the public. 

There are to-day about 200 patents on various forms of 
electric heating and cooking devices. The usual form of 
electric street car heater, takes from two to five amperes 
at 500 volts pressure, and after a street car is once heated, 
from 1200 to 1500 watts of current will provide enough 
heat for the coldest weather. In a large electric street 
railway plant, the current will cost about three cents an 
hour per car to keep the heaters in operation, and this 
figure will be found to be little if any more than stoves 
using anthracite coal for fuel. The heaters are usually 
placed under the seats and are of course out of the way 
of passengers. A large number of street railways are 
now using them. 

Cooking by means of electricity is being advocated by 
several companies and without doubt there are many 
cases where electric cooking devices can be used at a cost 
of operating about on a par with coal stoves. 



IU6 HKATING AND METAI. WORKING. 

Quite a number of patents have been taken out on 
heaters designed for alternating current work whose 
operation depends on the setting up of eddy or secondary 
currents in cores of coils of wire carrying alternating 
current. Such a heater would not of course operate on 
direct current circuits. 

One of the most interesting applications of heat from 
electricity is that of metal working and welding. 

Electric welding machines are at present doing work 
that would have been practically impossible with forge 
and hammer. The Thomson electric welding machines 
use alternating current for welding purposes by sending 
an alternating current of moderately high pressure 
through the primary coil of a large converter, the sec- 
ondary of which furnishes a current of immense volume 
at a voltage of but a few volts. The pieces of metal 
to be united in the weld are placed in the secondary 
circuit by means of clamps, with their ends in contact 
with each other. The point of contact being the 
only appreciable resistance in the secondary circuit, the 
ends are at once raised to a high temperature. The cur- 
rent is then increased in the primary, and the junction 
of the two pieces of metal to be welded, is raised to a 
welding heat. While this heating is in progress, pres- 
sure is being applied so as to press the pieces to be 
welded into even more intimate contact. The whole 
operation of welding a large bar of iron occupies but a few 
seconds and the joint made, in many cases is found to be 
the strongest part of the bar. Many metals may be 
welded in this way which are very difficult or practicall y 
impossible to weld in any other way. Wrought iron pipe 
bent in various awkward shapes, may be united in this 



STATION INSTRUMENTS. 157 

way in a perfect manner, an operation which is often- 
times very expensive when done in the usual manner. 
Large crossing frogs and steel rails are often welded on 
the electrical welder. 

The intense heat of the voltaic arc is used to some 
extent in metal working. The usual plan is to make the 
metal on which the work is to be done, one pole, and a 
carbon provided with a flexible conducting cord and 
handle as the other pole, and form the arc between the 
metal body and the carbon. 

If a piece of metal be connected to one pole of a suitable 
source of current supply, and a pail of salt water be con 
nected to the other, it will be found that by dipping the 
end of the metal in the water that it may be raised to a 
wliite heat in a few minutes, the water still remaining cool. 
Tliis may seem impossible at first thought, but neverthe- 
less a fact. A large number of small arcs probably form 
between the metal and the water, and with metal pieces 
of proper size, they may be quickly raised to a high heat 

SWITCH BOARD AND STATION INSTRUMENTS. 

All electrical machinery should, when performing its 
usual duty, be capable of being controlled, started and 
stopped in an exact and simple manner, and to know 
whether a given dynamo or motor is performing its duty, 
there must necessarily be connected suitable measuring 
instruments. The proper fitting of a station switchboard 
is an extremely important consideration, for in many 
cases, without the use of simple and reliable means of 
dynamo regulation and control, a station could never 
perform its proper work. What we cannot see being devel- 
oped in machinery, we must have indicated by some means. 



158 STATION INSTRUMENTS. 

Bvery electric light or power station should be provid- 
ed with all instruments that are necessary for the gov- 
erning and regulating of its machinery. Ihere should 
be instruments which indicate the an.ount of load on the 
dynamos in amperes, also their p:essure in volts. 

The dynamo regulating apparatus may be either auto- 
matic or performed by means of rheostats, etc. Ground 
detectors should be used to detect or locate contacts 
between the wiring or dynamos and the ground. To 
prevent damage from lighting in the station, lighting 
arresters are placed on the lines exposed. Switches 
should be provided to connect the dynamos to the cir- 
cuits or to make various combinations of the dynamos 
and thus get various currents. 

Fuse or magnetic cutouts are used to prevent a load 
being applied to the dynamos beyond their maximum 
capacities. 

The switch boards themselves should be made of a 
non-combustible insulating material, such as marble or 
slate free from metallic veins, marble being the best 
possible material usually, for it has high insulating 
qualities and does not crack or chip as easily as the usual 
grade of slate generally used. "Marbleized" slate how- 
ever, is much superior to the usual slate and is larg^ely 
used. In the score of economy, wooden switch boards 
are often placed in otherwise first class plants. An oak 
or pine switch board in a plant using low voltage cur- 
rent, may undoubtedly be made reasonably safe, but it 
is an exceptional case when one is found, and as a rule 
a wooden switch board for high potential circuits, when 
made safe, will cost nearly as much as a slate or marble 
board. 



STATION INSTRUMENTS. 159 

There should always be from two to three feet space 
behind a switch board and it should be kept free from 
waste material from the plant. Station electricians often 
pile or throw everything imaginable behind them and 
when trouble comes behind the board, it is a hard job to 
do anything in a quick manner. Many of the larger 
electric light companies are building and selling very 
superior switch boards at reasonable figures. 

Rheostats or Field regulators used with shunt or com- 
pound wound dynamos provide means of regulating their 
output by varying the current through the field windings. 
They usually consist of a series of resistances in the form 
of German silver or iron wire coils that are connected at 
several points to contacts on the face of the rheostat, and 
by means of a contact brush rubbing on their surfaces^ 
more or less resistance is put in series with the dynamo 
field circuit. 

Rheostats of this description are very clumsy, and a 
better type now produced, is the enamel or cement rheo- 
stat in which the resistance wires are imbedded in cement 
or enamel, only a small amount of wire being required, 
and that very small in size, as it is well known that a 
wire imbedded in such a manner will carry a current 
Several times greater than in open air. They occupy but 
little room and are compact and fire proof. 

Quite often in central stations where circuits are une- 
qually loaded, it becomes necessary to raise the potential 
on individual feeders. To increase the potential of the 
dynamo would not sufi&ce because circuits having a light 
load would have too high a pressure. The **booster" for 
direct current circuits consist of a small series dynamo 
placed in series with the circuit whose pressure is to be 



l6o STATION INSTRUMENTS. 

raised. The conductors on its fields and armature are 
sufficiently large enough to carry full current. An 
increase of current in the series field would mean an 
increase in potential at the armature and this added to 
the potential of the generator gives the desirable pres- 
sure. This machine increases the pressure automatically 
as the current increases. 

For alternating circuits, this scheme is not possible, 
but the flexibility of the transformers is admirably 
utilized by Mr. L. B. Stillwell in the Stillwell regulator 
and described by him as follows: '*If each supply circuit 
receives current from an independent generator, that is, 
a generator which is called upon to furnish current 
to other supply circuits, the necessary adjustment of 
pressure is obtained by regulating the field charge of the 
generator by means of the rheostat provided for that 
purpose. If however, several supply circuits are receiv- 
ing current from the same generator, it becomes neces- 
saiy to provide means for adjusting the pressure of each 
without disturbing the others. The regulator consists of 
a transformer having a secondary coil adjustable in 
length. Connections are brought out from dififerent 
points on the secondary coil, to a multi point switch, by 
means of which the secondary coil, or any portion of it^ 
may at will, be thrown in series with the supply circuit. 
When this is done, the electro-motive force due to the 
whole or a part of the secondary coil of the regulator is 
added to the initial potential of the circuit. The 
potential of tbe supply circuit may therefore be acurately 
adjusted, independent of whatever may be the potential 
at the terminals of the generator". 

An instrument, the Compensator, is always used with 



STATION INSTRUMENTS. l6l 

the regulator and in the same circuit. It consists of a 
small transformer which supplies current to the volt- 
meter. The primary circuit has two windings, one of 
which is on the usual high pressure constant potential 
circuit and the other is a winding in series with the 
circuit whose voltage is to be measured. 

The secondary circuit supplies current to the voltmeter 
and when current is flowing, a current is induced on the 
secondary coil from the primary, which causes voltage to 
be shown at the voltmeter, corresponding correctly to 
the voltage at the end of the line with that current. To 
sum it up, the compensator acts upon the voltmeter to 
give the potential at the end of the line. 

Voltmeters and ammeters are of two general t3rpes, 
those whose reading is due to magnetic effects and those 
whose reading depends on the expansion and contraction 
of a wire due to current passing through, and heating it. 

The measuring instruments using magnetism, are of 
various types, some of them using a simple selonoid of 
wire acting on a movable iron core, to which is attached 
the indicating pointer. In instruments of this type for 
use on alternating current, the selonoid spool, if made of 
metal, is always slit to prevent the spool acting as a sec- 
ondary coil of low resistance, in which currents would be 
generated by the passage of current through the coil 
windings. The iron core of such a coil would have to be 
laminated, or built up of small iron wires to prevent cur- 
rents being generated in it. 

Other magnetic instruments use the effect obtained by 
mounting a small armature between the pole pieces of a 
permanent horse-shoe magnet, and sending the current 
to be measured through the armature, which tends to 



I62 STATION INSTRUMENTS. 

revolve on its shaft and thus produce a movement which 
gives the reading. Such instruments are usually pro* 
vided with jeweled bearings and are quite expensive, biv 
the leading measixring instruments of this type, the 
Weston ammeters and voltmeters, are the standard instru- 
ments to-day in America for direct current measuring. 

The *'hot wire" instruments are mainly used for alter- 
nating current work, for since the heating effect of a 
given current is the same for either direct or alternating 
current, it follows that such an instrument should be 
well adapted to the measurement of alternating current. 

All high grade instruments should be very carefully 
handled and in case repairs are needed, it should be done 
only by one thoroughly acquainted with the work. The 
rougher classes of cheap instruments are ofted found to 
be incorrect and it is always policy to calibrate them by 
means of a standard instrument as often as possible. 

In selecting a switch board ammeter or voltmeter, an 
illuminated scale with large figures is preferable. Dead- 
beat instruments should be used as much as possible as 
an instrument whose pointer comes at once to the 
correct reading and stays there without needless 
swinging, saves time, and is by far preferable to those 
whose needle swings to and fro before coming to the 
exact reading. All instruments should be placed in such 
a position as to be easily seen by the dynamo tender, but 
should not be placed in such close proximity to a dyna- 
mo, as to have its magnetism effect the reading. In case 
of it being impossible to place them away from the vicin- 
ity of a dynamo, they should be provided with magnetic 
shields, which may be made in various forms. 

Voltmeters should be chosen having as high a resi»- 



STATION INSTRUMENTS. 1 63 

tance as possible, and ammeters should have the least 
possible resistance, for it will be found that station 
instruments often take many times more current to 
operate them than should be used on proper instruments. 

In placing instruments on a switch board, care should 
be taken to so place them that their needles or pointers 
will be at zero when no current is flowing. Direct read- 
ing instruments are always to be preferred to those read- 
ing in * 'degrees", etc. A voltmeter should read directly 
in volts, and an ammeter in amperes, or a resistance 
measuring instrument in ohms. 

All electric light or power stations having conductors 
in the open air, must have devices to protect the dynamos 
from injury from lightning. It should not be understood 
that lightning must actually strike a line to injure the 
apparatus connected to it. The majority of cases of 
trouble from lightning occur from currents of high volt- 
age induced in the line by the passage of lightning 
through the air near or parallel to the line. The voltage 
is generally very high, and ruined armatures and field 
coils result unless means for protection are employed. 

In many cases the actual damage to the dynamo is 
caused by the dynamo current following the high voltage 
lightning discharge, and the damage is done before the 
dynamo can be stopped. A great deal of time and ingen- 
uity has been spent in devising various lightning arrest- 
ers. To be^ reliable, a lightning arrester should always 
be ready to operate. It should allow the lightning to 
pass to the groimd, but at the same time prevent the dy- 
namo current following. The lightning takes the path 
of least resistance to ground and will of course break 
tnrough the system at its weakest point. 



164 STATION INSTRUMENTS 

The term resistance'* as here used does not necessar 
ily mean the ohmic resistance but the sum of the ohmic 
resistance and the impedance due to the self-induction of 
the circuit. A lightning discharge rather than pass 
through a coil of even very low resistance will often jump 
a large air gap and pass to the ground. 

The lightning arrester usually places a small air gap 
between the systems and the ground, and this is designed 
to be the path of least resistance to ground. After a dis- 
charge takes place across the air gap to ground the next 
operation is to interrupt the dynamo current which we 
have said, usually follows. 

This is accomplished in various ways, one of the most 
common being to place the air gap near the poles of a 
small electro magnet, which ** blows'* out the arc by 
means of the magnetism, it being a well known fact that 
if a magnet is placed near an arc so that the arc is in the 
magnetic field that the arc will be apparently blown aside 
as if it were in a strong current of air. By using a strong 
magnetic field in this way, an arc may be instantly inter- 
rupted and blown out. Another method is to have the air 
gap over which the arc would i*tart, inclosed in an air 
tight box and as soon as an arc 1:1 started, the confined 
air immediately expands due to the heat of the arc, and 
operates suitable mechanism for breaking the circuit. 

The air gap may be made between two terminals made 
of non arcing metal and thus make it impossible to main- 
tain an arc. The non-arcing metal is an alloy lately dis- 
covered which apparently on being melted by the arc. 
forms a gas having a high resistance, for a few small air 
gaps in series between pieces of this alloy, will rupture 
an arc on the highest pressure used for commercial eieC' 
trie lightin|?5. 



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COPPER WIRE TABLE. 

Giving weights, lengths and resistances for A. W. G. TBrown and Sharpe) Guage. 



GUAGE, 

To the nearest 

fourth significant 

digit. 






0000 

000 

00 



1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

16 

16 

17 

.} 

30 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

32 

33 

34 

35 

36 

37 

38 

39 



Diam- 
eter. 
Inches. 



0.460 
0.4096 
0.3648 
0.3249 
0.2893 
0.2576 
0.2294 
0.2043 
0.1819 
0.1620 
0.1443 
0.1285 
0.1144 
0.1019 
0.09074 
0.08081 
0.07196 
0.06408 
0.05707 
0.05082 
0.04526 
0.04030 
0.03589 
0.03196 
0.02846 
0.02635 
0.02267 
0.03010 
0.01790 
0.01594 
0.0142 
0.01264 
0.01126 
0.01003 
0.008928 
0.007950 
0.007080 
0.006305 
0.005615 
0.0050 
0.004453 
0.003965 
0.003531 



4010.003145 



Area 
Circu- 
lar 
mils. 



211,600 
167,800 
133,100 
105,500 
83,690 
66,370 
62,630 
41,740 
33,100 
26 250 
20,820 
16 510 
13,090 
10,380 
8,234 
6,530 
5,178 
4,107 
3,257 
2.683 
2,048 
1,624 
1,288 
1,022 
810.1 
642.4 
509.5 
404.0 
320.4 
254.1 
201.5 
159.8 
126.7 
100.5 
79.70 
63.21 
60.13 
39.75 
31.62 
26.0 
19.83 
15.72 
12.47 
9.888 



WEIGHT. 



I<bs. per 
foot. 



0.6406 

0.6080 

0.4028 

0.3195 

0.2533 

0.2009 

0.1593 

0.1264 

0.1002 

0.07946 

0.06302 

0.04998 

0.03963 

0.03143 

0.02493 

0.01977 

0.01568 

0.01243 

0.009858 

0.007818 

0.006200 

0.004917 

0.003899 

0.003092 

0.002452 

0.001945 

0.001W3 

0.001223 

0.0009699 

0.0007692 

0.0006100 

0.0004837 

0.0003836 

0.0003042 

0.000^13 

0.0001913 

0.0001617 

0.0001203 

0.00009543 

0.00007568 

0.00006001 

0.00004759 

0.00003774 

0.00002993 



lybs. per 
Ohm. 

@50°C. 
122° Fah. 



11.720 

7,369 

4,634 

2,914 

1,833 

1,163 
726.0 
456.9 
286.7 
180.3 
113.4 

71.33 

44.86 

28.21 

17.74 

11.16 
7.017 
4.413 
2.776 
1.746 
1.098 
0.6904 
0.4343 
0.2731 
0.1717 
0.1080 
0.06793 
0.04272 
0.02687 
0-01690 
0.01063 
0.006683 
0.004203 
0.002643 
0.001662 
0.001045 
0.0006575 
0.0004135 
0.0002601 
0.0001636 
0.0001039 
0.00006454 
0.00004068 
0.00003.559 



I.ENGTH. 



Feet 
per lb. 



1.661 
1.969 
3.483 
3.130 
3.947 
4.977 
6.276 
7.914 
9.980 
12.58 
15.87 
20.01 
25.23 
31.82 
40.15 
60.59 
63.79 
80.44 
101.4 
127.9 
16^.3 
20J.4 
266.6 
323.4 
407.8 
514.3 
648.4 
817.6 
1,031 
1,300 
1,639 
2,067 
2,607 
3,287 
4,145 
6,227 
6,691 
8,311 
10,480 
13,210 
16,660 
21,010 
26,500 
33.410 



Ft. per 
Ohm. 

@50°C. 
122°Fah 



RESISTANCE. 



Ohms 
per lb. 

@ 50° C. 
122° Fah. 



0.00008536 
0.0001357 
0.0003158 
0.0003431 
0.00054.56 
0.0008675 
0.001379 
0.003193 
0.003487 
0.005545 
0.008817 
0.01402 
0.03239 
0.03545 
0.05636 
0.08963 
0.1426 
0.2266 
0.3603 
0.5729 
0.9109 
1.448 
2.303 
3.663 
6.823 
9.2,59 
14.73 
23.41 
37.22 
59.18 
94.11 
149.6 
237.9 
378.3 
601.6 
956.5 
1,531 
3,418 
3,845 
6,114 
9,722 
15,4911 
34,580 
39.080 



Ohms 
per foot. 

@60°C. 
i22R Fah. 



0.00005467 

0.00006893 

0.00008692 

0.0001096 

0.0001382 

0.0001743 

0002198 

0.0003771 

0.0003495 

0.0004406 

0.0005556 

0.0007007 

0.00088ai 

0.001114 

0.001405 

0.001771 

0.003334 

0.003817 

0.003553 

0.004479 

0.005648 

0.007133 

0.008980 

0.01133 

0.01428 

0.01801 

0.02271 

0.02863 

0.03610 

0.O4562 

0.05740 

0.07239 

0.09128 

0.1151 

0.1451 

0.1830 

0.2308 

0.3910 

0.3669 

0.4637 

0.5836 

0.7357 

0.9277 

1.17C 



r.i,^^fl5i^r^'^^^ of copper=8.89. Resistance in terms ot the international 
ohm, Irom American Institute of Electrical Engineers TransactionOct. 1893 



COPPER WIRE DATA 



167 



Safe Carrying Capacity Table. 



Below is a table showing the safe carrying capacity of dif- 
ferent sizes of Brown & Sharpe gauge copper wires and cables 
of ninety-eight per cent conductivity. Taken from Rules 
and Requirements of the National Board of Underwriters 





Table A. 


Table B. 






Table A. 


Table B. 


B. &S. 


Rubber 


Other 


Circular 


Circular 


Rubber 


Other 




Insula- 


Insula- 






Insula. 


Insula- 


Gauge. 


tion. 


tions. 


Mills. 


Mills. 


tion. 


tions. 




Amperes. 


Amperes. 






Amperes. 


Amperes. 


18 


3 


5 


1,624 


200,000 


200 


300 


16 


6 


10 


2,583 


300,000 


275 


400 


14 


15 


20 


4,107 


400,000 


325 


500 


12 


20 


25 


6,530 


500,000 


400 


600 


10 


25 


30 


10,380 


600,000 


450 


680 


8 


35 


50 


16,510 


700,000 


500 


760 


6 


50 


70 


26,250 


800,000 


550 


840 


5 


55 


80 


33,100 


900,000 


600 


920 


4 


70 


90 


41,740 


1,000,000 


650 


1,000 


3 


80 


100 


52,630 


1,100,000 


690 


1,800 


2 


90 


125 


66,370 


1,200,000 


730 


1,150 


I 


100 


150 


83,690 


1,300,000 


770 


1,220 





125 


200 


105,500 


1,400,000 


810 


1,290 


00 


150 


225 


133,100 


1,500,000 


850 


1,360 


000 


175 


275 


167,800 


1,600,000 


890 


1,430 


0000 


225 


325 


211,600 


1,700,000 
1,800,000 
1,900,000 
2,000,000 


930 

970 

1,010 

1,050 


1,490 

1,550 
1,610 
1,670 



For insulated aluminum wire the safe carrying capacity is 
eighty-four per cent of that given in the above tables for 
copper wire with the same kind of insulation. 



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